Ionic currents during the action potential in the molluscan neurone with the self-clamp technique

The ionic currents during the action potential in the F1 neurone of Helix aspersa were investigated, using the Self-Clamp Technique. A spontaneous action potential was recorded and then replayed, both in its direct and in its inverted form, to the same cell in voltage clamp and in control conditions. Under various experimental conditions such as treatment with the specific ionic channels blockers tetrodotoxin, lanthanum, 4-aminopyridine or tetraethylammonium, as well as low sodium and low calcium external media, the single ionic currents were detected by stimulating the membrane with the direct pulse only. The Self-Clamp Technique allowed the measuring of the following parameters, in their real time course during the action potential: a) the total action currents; b) the pharmacologically blocked ionic components; c) the ionic components which remained insensitive to the agents used (residual currents). These data were compared with those obtained by applying conventional rectangular pulses in voltage clamp. The membrane capacity was measured with the Self-Clamp Technique and the recorded currents were normalized assuming a specific capacity of 4 μF/cm². The isolated ionic components were directly compared with the total action currents to evaluate the degree to which blockage was complete. The electric charge transported by each ionic specimen was evaluated as well as the individual ionic amounts. The sodium influx was 3.18 ± 0.55 pM/cm² per impulse (9 cells), calcium influx 1.03 ± 0.37 pM/cm² per impulse (10 cells). A value of 6.37 ± 1.03 pM/cm² per impulse was found for the potassium outflux, with a probable overestimation of about 1 pM/cm² per impulse (9 cells).     

An electrophysiological study of the membrane properties of the immature and mature oocyte of the Batstar,Patiria miniata

Immature oocyte membrane properties of a starfish, Patiria miniata, were investigated by microelectrode techniques. The resting membrane potential in artificial seawater (ASW) was ?78.5 ± 6.7 mV (n = 61, inside negative). This was mainly accounted for by a selective permeability to potassium ions. Potassium ion-selective microelectrodes were used to measure intracellular K⁺ ion activity, which was 350 mM. The sodium to potassium permeability ratio was 0.02 ± 0.01 (n = 4). The current-voltage relation was nonlinear. The I–V curve included both areas of inward and outward rectification. The dependence of inward rectification upon the K⁺ ion electrochemical gradient was demonstrated. The membrane was capable of a regenerative action potential due to permeability changes for Ca²⁺ and Na⁺ ions. The Ca and Na components of the action potential were identified. The Ca component was reversibly suppressed by cobalt and irreversibly blocked by D-600. The Na component was tetrodotoxin (TTX) insensitive. The excitable response of P. miniata oocytes is similar to that described by Miyazaki et al. (1975a) for those of the starfish Asterina pectinifera.Immature oocytes were stimulated to mature with 10^?5M 1-methyladenine (1-MA) during continuous monitoring of the membrane potential. The resting potential in ASW became more inside negative during maturation. This change of the passive membrane property of the oocyte may be accounted for by the increased selectivity to K⁺ ions. The specific membrane resistance near the resting potential increased from 4.2 ± 1.4 to 21 ± 8.7 kΩ·cm² (n = 15) during maturation, while the specific membrane capacitance decreased slightly from 2 ± 0.5 to 1.7 ± 0.6 μF/cm² (n = 5). Maturation had little effect upon the active membrane properties.     

Studies of excitable membrane formed on the surface of protoplasmic drops isolated from Nitella III. Impedance of the surface membrane

A protoplasmic drop isolated from an internodal cell of Nitella in an initial solution composed of 70 mM KNO₃, 50 mM NaNO₃ and 5 mM CaCl₂ became electrically excitable when the drop was placed in the final solution containing 0.5 mM KNO₃, 0.5 mM NaCl, 1 mM Ca(NO₃)₂ and 2 mM Mg(NO₃)₂. The electrical impedance of the surface membrane of the drop was measured both in the initial and final solutions at frequencies between 60 Hz and 100 kHz.The impedance and admittance loci of the surface membrane fell on circular arcs. The d.c. resistance R_m°, and the d.c. capacitance C_m° were determined by extrapolating the circular arcs to the low frequency limit. R_m° thus determined was in the range of 50–200 Ω·cm² in the initial solution, and increased to a steady value of 0.4–4.0 kΩ·cm² when the external solution was replaced by the final solution. After the protoplasmic drop was isolated from the internodal cell of Nitella, C_m° decreased monotonically from about 1.5 μF/cm² within 20 min and approached $\text{1.25±0.1 μ}\text{F/cm}{}^2$ both in the initial and final solutions. No appreciable difference was observed for C_m° in these two solutions.The impedance data were discussed in relation to the process of formation of the membrane at the surface of the protoplasmic drop. After the excitable stage was reached, the drop membrane impedance was found to decrease by a factor of 10 during excitation.     

Maturation and fertilization of the sea urchin oocyte: An electrophysiological study

Some electrical properties of the sea urchin oocyte during germinal vesicle breakdown (GVBD) and fertilization have been studied using two intracellular electrodes. Oocytes with distinct germinal vesicles have resting potentials of ?70 to ?90 mV and the specific membrane resistance may range from 3 to 10 kΩ·cm². Around rest the I–V relationship is concave toward the axis origin and the membrane is K⁺ selective. A second electrical state, of lower potential and higher resistance, preexists in the membrane. Following GVBD, the K⁺-selective system is lost and the oocyte attains the characteristics of the second state with a resting potential of ?10 to ?50 mV and specific membrane resistance of 10–50 kΩ·cm². At rest the I–V relationship tends to be convex toward the axis origin. The majority of sea urchin eggs (which have undergone GVBD and completed meiosis) have a resting state of ?10 to ?30 mV; 10–50 kΩ·cm². The I–V relationship around rest is convex toward the axis origin and the resting potential is sensitive to changes of Na⁺, Cl^?, and K⁺ in the external medium. There is probably no major change in the electrical properties of the oocyte during the completion of meiosis. A small percentage of eggs from suboptimal animals have high resting potentials of ?70 to ?90 mV and specific membrane resistance of 5–50 kΩ·cm². Such eggs have predominantly K⁺-selective membranes and we suggest that they are either underripe or aged. The first electrical event across the egg plasma membrane during fertilization is a step-like depolarization which occurs about 2 sec after the attachment of the fertilizing spermatozoon to the vitelline layer. There is no change—at the level of the light microscope—either in the egg surface or in the behavior of the spermatozoon until the second event, the fertilization potential (FP), is initiated 11 sec later. The cortical reaction occurs simultaneously with the FP and during the rising phase of the FP the spermatozoon stops gyrating around its point of attachment. Oocytes, which do not have cortical granules, upon insemination exhibit step events but no FP; in contrast artificially activated eggs, either spontaneous or induced by the ionophore A23187, give rise to only the FP. We suggest that the FP is the electrical result of the modification of the egg plasma membrane during cortical exocytosis.     

Extracting cancer cell line electrochemical parameters at the single cell level using a microfabricated device

Cancer cells have distinctive electrochemical properties. This work sheds light on the system design aspects and key challenges that should be considered when experimentally analyzing and extracting the electrical characteristics of a tumor cell line. In this study, we developed a cellularbased functional microfabricated device using lithography technology. This device was used to investigate the electrochemical parameters of cultured cancer cells at the single-cell level. Using impedance spectroscopy analyses, we determined the average specific capacitance and resistance of the membrane of the cancer cell line B16-F10 to be 1.154 ± 0.29 μF/cm², and 3.9 ± 1.15 KΩ.cm² (mean ± SEM, n =14 cells), respectively. The consistency of our findings via different trails manifests the legitimacy of our experimental procedure. Furthermore, the data were compared with a proposed constructed analytical-circuit model. The results of this work may greatly assist researchers in defining an optimal procedure while extracting electrical properties of cancer cells. Detecting electrical signals at the single cell level could lead to the development of novel approaches for analysis of malignant cells in human tissues and biopsies.     

The electrical changes accompanying fertilization and cortical vesicle secretion in the medaka egg

The electrical properties of the egg of the medaka, Oryzias latipes, were studied before, during, and after fertilization. The resting potential of the unfertilized egg averaged ?39 ± 9 mV in Yamamoto's Ringers (Y. Ringers), but 20% of the values were between ?50 and ?60 mV. Fertilization triggers a small depolarization of 4 ± 3 mV in 10% Y. Ringers with an average duration of 20 ± 10 sec. The amplitude of this depolarization is independent of [Na⁺]_o, [Ca²⁺]_o, and [Cl^?]_o, so it appears to be due to a nonspecific leak triggered by sperm-egg fusion. The depolarization is followed by a longer hyperpolarizing phase with an average amplitude of 31 ± 12 mV. Recovery from this hyperpolarization has a fast phase lasting 155 ± 18 sec, followed by a slower phase which reaches a steady average membrane potential of ?19 ± 1 mV by 9 min after fertilization. The membrane resistance falls 10-fold during the first 2 min after fertilization, from 40 (1520 kΩ-cm²) to 3 MΩ. This is largely due to an increase in the K⁺ conductance. At the peak of the hyperpolarization, the membrane potential exhibits a 28 mV/decade [K⁺]_o dependence and a 6 mV/decade [Na⁺]_o dependence. The membrane resistance slowly recovers over the next 8 min to a value about 30% larger than before fertilization. The relation of current vs voltage was linear before, during, and after fertilization and indicated a reversal potential of ?98 ± 20 mV for the hyperpolarization peak. The egg's capacitance averaged 0.04 ± 0.01 μF (0.9 μF/cm²) before fertilization and approximately doubles within 90 sec after fertilization. It then decreases over a 9-min period, reaching a value 25% smaller than before fertilization.     

Biophysical properties of human astrocytic brain tumor cells in cell culture

For malignant cells cultured from a human astrocytoma, electrophysiological characteristics of the plasma membrane included specific resistivity of 446.82 ± 279.5 ohm·cm², specific capacitance of 0.758 ± 0.52 microfarads/cm², time constant 0.318± 0.10 msec. The resting membrane potential averaged-14.07 ± 7.4 mV; the mean input resistance 8.1 ± 4.0 megohms. The average cell area was 1638 ± 585 ±² for contactual and 1919 ± 989 ±² for noncontactual cells. Changes in input resistance and resting membrane potential were observed with increasing time in culture, possibly reflecting cell cycling. There did not appear to be electrical coupling in this cell line.     

External Mg2+ is required for hyperpolarization to occur in ovulated oocytes of the prawn Palaemon serratus

Immediately after dissection, the ovulated oocyte of the prawn Palaemon serratus had a resting potential E_m of −42 ± 2 mV and a membrane resistance R_m of 15 ± 5 MΩ; the membrane was more permeable to Cl⁻ than to K⁺. The oocyte spontaneously hyperpolarized and E_m gradually reached −70 mV 20–30 min after removal of the oocyte from the female, due to increased membrane permeability to K⁺. However, the hyperpolarization occured only if Mg²⁺ was present in the seawater; external Ca²⁺ was not required. Long-term incubation without external Mg²⁺ depolarized the membrane and increased membrane resistance. After preincubation in Mg²⁺-free ASW, oocytes transferred to standard artificial seawater (ASW) transiently hyperpolarized and then repolarized, before gradually hyperpolarizing to a sustained value of −62 ± mV. The respective roles of external Mg²⁺ and fertilization in eliciting the electrical response of the prawn egg at natural spawning are discussed.     

Membrane potential of the unfertilized sea urchin egg

The membrane potential, specific resistance, and potassium selectivity of the unfertilized Strongylocentrotus purpuratus egg were determined by two independent methods: tracer flux and microelectrode. The potassium influx was 0.50 ± 0.2 pmole/cm²· sec, which was greater than the sodium, chloride, and calcium influxes by factors of 4, 7, and 75, respectively. By means of the constant-field equations, the flux data were used to calculate membrane potential (?70 mV) and specific resistance (420 kΩ · cm²). The effect of the external potassium concentration on the sodium influx was determined and the results closely fit the result expected if the membrane behaved as a potassium electrode. Microelectrode measurements of the potential and resistance were ?75 ± 3 mV and 380 ± kΩ · cm².     

Some electrophysiological and permeability properties of the mouse egg

Certain electrophysiological and ionic properties of the mouse egg (CF-1 and BDF 12–18 hr post ovulation) have been investigated. Membrane potential (?14 ± 0.4 mV, ± SE, inside negative), membrane resistance (2610 ± 38 ohm·cm²), and membrane capacitance (1.6 ± 0.03 μF cm^?2) have been determined by means of intracellular microelectrode recording techniques. Membrane potential and related parameters are stable for extended periods of time upon impalement and the magnitude of the cell membrane potential has been demonstrated to be sensitive to alteration in external sodium. The electrophysiological studies in conjunction with measurements of unidirectional potassium fluxes using isotope tracer-techniques have allowed determination of membrane permeability to potassium (8 × 10^?8 cm sec^?1) and membrane potassium conductance (25 μmho cm^?2). Furthermore, the use of tracer flux techniques has indicated that the exchangeable fraction of intracellular potassium is 204 ± 14 mM. This represents the bulk of egg potassium (222 ± 19 mM as determined from flame photometry). Studies of unidirectional potassium efflux have indicated that its movement out of the egg is made up of at least two components; an external potassium-independent potassium efflux and external potassium-dependent efflux, the latter possibly representing a potassium exchange mechanism. The combined electrophysiological and tracer-flux data indicate that only a small portion of the total membrane conductance is composed of potassium conductance at this stage of development. This and the fact that the membrane potential is far from the potassium equilibrium potential are similar to observations made on mature eggs of several other species.     

ELECTRIC IMPEDANCE OF NITELLA DURING ACTIVITY

The changes in the alternating current impedance which occur during activity of cells of the fresh water plant Nitella have been measured with the current flow normal to the cell axis, at eight frequencies from 0.05 to 20 kilocycles per second, and with simultaneous records of the action potential under the impedance electrodes. At each frequency the resting cell was balanced in a Wheatstone bridge with a cathode ray oscillograph, and after electrical stimulation at one end of the cell, the changes in the complex impedance were determined from the bridge unbalance recorded by motion pictures of the oscillograph figure. An extension of the previous technique of interpretation of the transverse impedance shows that the normal membrane capacity of 0.9 µf./cm.² decreases about 15 per cent without change of phase angle, while the membrane resistance decreases from 10⁵ ohm cm.² to about 500 ohm cm.² during the passage of the excitation wave. This membrane change occurs during the latter part of the rising phase of the action potential, and it is shown that the membrane electromotive force remains unchanged until nearly the same time. The part of the action potential preceding these membrane changes is probably a passive fall of potential ahead of a partial short circuit.     

Enhancement in the Transdermal and Localized Delivery of Honokiol Through Breast Tissue

Honokiol is a natural phenolic anti-cancer compound isolated from an extract of seed cones from Magnolia grandiflora. This study investigated the transdermal delivery of honokiol using various enhancement methods and to explore the potential of honokiol to treat breast cancer directly via delivery through mammary papilla. Poration of dermatomed human skin with microneedles significantly increased the delivery of honokiol by nearly 3-fold (97.81?±?18.96 μg/cm²) compared with passive delivery (32.56?±?5.67 μg/cm²). Oleic acid was found to be the best chemical penetration enhancer, increasing the delivery almost 27-fold (868.06?±?100.91 μg/cm²). Addition of oleic acid also resulted in better retention of drug in the porcine mammary papilla (965.41?±?80.26 μg/cm²) compared with breast skin (294.16?±?8.49 μg/cm²). Anti-cancer effect of honokiol was demonstrated with the decrease in the release of cytokine IL-6 and further suppression of Ki-67 proliferative protein. In addition, the topical honokiol formulation investigated was found to be safe and non-irritant. In summary, both microneedles and chemical enhancers can improve the absorption of honokiol through skin. Directly applying honokiol on mammary papilla is a potential administration route which can increase localized delivery into breast tissue.     

Electrical properties of the body wall of Hydra

If the hydrostatic pressure in the enteron of Hydra is made more than 2–4 mm of water greater than the outside pressure, the animal becomes distended, indicating that the normal enteron pressure is less than this. Positive enteron pressure attenuates the spontaneous, negative-going electrical spikes across the body wall, which are called contraction pulses (CP''s) because of their relation to column contraction. Pressure has little effect on the transepithelial resting potential. The low frequency electrical impedance of the column is nonlinear. The impedance tends to increase as the transepithelial potential is made more negative. The nonlinearity has both initial and delayed components. The DC impedance of the column near the resting potential averages 100 kohms (approximately 5 kohms-cm²). The phase between transepithelial potential and imposed sinusoidal current approaches -90° with increasing current frequency. Bode plots of the column impedance and the phase lag indicate that the column has three or more time constants. CP''s show several unusual features: (a) their amplitude and frequency are essentially independent of the transepithelial potential when the latter is altered by imposed current; (b) there is practically no change in column impedance during CP firing; (c) when the transepithelial potential is clamped at zero, CP''s continue to appear spontaneously as current spikes. These features are consistent with the hypothesis that the CP-generating membrane forms but a small fraction of the total transverse impedance of the column.     

Application of the Hodgkin-Huxley equations to an electric field model for interaction between excitable cells

We previously described a model for the electrical transfer of excitation from one cell to the next which utilized the electric potential generated in the junctional cleft between the cells. Low-resistance connections between the cells were not used in the model, and it was assumed that the junctional membranes were excitable. This model was analyzed for the static case without capacitances and for the dynamic case in which capacitances were part of the circuit elements. For simplicity, the Na⁺ resistance (R_Na), after a threshold potential was exceeded, was allowed to decrease exponentially (to 1% of its initial value) within 0·25–1·0 ms, and possible changes in the K⁺ resistance were ignored. In this paper, we have incorporated the Hodgkin-Huxley equations into the operation of the lumped membrane units for the electrical equivalent circuit of the cell membrane. The parameters varied are the membrane capacitances, resistances, maximum Na⁺ conductance ($\text{g}{}_{\mathrm{<mtext>Na</mtext>}}$), and the radial cleft resistance (R_jc). We demonstrated that our model worked very well, i.e. the successful transfer of action potentials was achieved, with the membrane units following Hodgkin-Huxley dynamics for changes in g_Na and g_K. The calculations indicate that transmission is facilitated when the junctional units have a higher $\text{g}{}_{\mathrm{<mtext>Na</mtext>}}$ and a lower capacitance and when R_jc is elevated. Lowering the resistance of the junctional membrane units several fold, relative to the surface membrane units, also facilitated transmission; however, the absolute resistance of the junctional membrane was still well above the maximum value that would allow sufficient local-circuit current to flow to effect transmission. Thus, the electric field model provides an alternative means of cell-to-cell propagation between myocardial cells which is electrical in nature but does not require the presence of low-resistance connections between cells.     

Characterization of the plasma-membrane H+-ATPase from Vicia faba guard cells

Stomatal movement is controlled by external and internal signals such as light, phytohormones or cytoplasmic Ca²⁺. Using Vicia faba L., we have studied the dose-dependent effect of auxins on the modulation of stomatal opening, mediated through the activity of the plasma-membrane H⁺-ATPase. The patch-clamp technique was used to elucidate the electrical properties of the H⁺-ATPase as effected by growth regulators and seasonal changes. The solute composition of cytoplasmic and extracellular media was selected to record pump currents directly with high resolution. Proton currents through the ATPase were characterized by a voltage-dependent increase in amplitude, positive to the resting potential, reaching a plateau at more depolarized values. Upon changes in extracellular pH, the resting potential of the cell shifted with a non-Nernst potential response (±21 mV), indicating the contribution of a depolarizing ionic conductance other than protons to the permeability of the plasma membrane. The use of selective inhibitors enabled us to identify the currents superimposing the H⁺-pump as carried by Ca²⁺. Auxinstimulation of this electroenzyme resulted in a rise in the outwardly directed H⁺ current and membrane hyperpolarization, indicating that modulation of the ATPase by the hormone may precede salt accumulation as well as volume and turgor increase. Annual cycles in pump activity (1.5–3.8 μA · cm^-2) were expressed by a minimum in pump current during January and February. Resting potentials of up to -260 mV and plasmamembrane surface area, on the other hand, did not exhibit seasonal changes. The pump activity per unit surface area was approximately 2- to 3-fold higher in guard cells than in mesophyll cells and thus correlates with their physiological demands.     

Electrogenic Na?K pump current in rat skeletal myoballs

Catecholamines and insulin have been reported to hyperpolarize skeletal muscle fibers via stimulation of the electrogenic Na-K pump (Flatman and Clausen, 1979, Nature, 281:580–581). Therefore, the electrogenic Na-K pump current was investigated in cultured colcemid-treated rat skeletal myoballs using whole-cell voltage clamp. Skeletal muscles were taken from newborn rat hindlegs, trypsin digested, and cultured. By day 7, all myoblast cells fused into myotubes. After treatment with the microtubule disrupter colcemid (10^?7 M) for 2 days, some of the myotubes became transformed into spherical myoballs, having an average diameter of 41.2 ± 1.5 μm (n = 21). The resting membrane potential averaged -56.8 ± 1.7 mV (n = 40). Ouabain (1 mM) quickly depolarized the myoballs to -51.1 ± 1.1 mV (n = 27), showing the existence of an electrogenic Na-K pump in the skeletal myoball preparation. The values for the specific membrane resistance and capacitance were 5.5 ± 1.0 KΩ-cm² (n = 21) and 3.7 ± 0.3 μF/cm² (n = 21), respectively. The pump current averaged 0.28 ± 0.03 pA/pF (n = 10), with the membrane potential at -60 mV and 10 mM intrapipette Na⁺. The Na-K pump contribution to resting membrane potential was calculated to be 5.7 mV, matching the ouabain-induced rapid depolarization. When the Na-K pump was stimulated with 50 mM intrapipette Na⁺, the pump current was about doubled (0.52 ± 0.08 pA/pF; n = 10). Isoproterenol (1 μM) and 8-Br-cAMP (1 mM) also significantly increased pump current by 50% (0.42 ± 0.04 pA/pF; n = 9) and 64% (0.46 ± 0.09 pA/pF; n = 7), respectively. In contrast, although insulin and phorbol ester also increased pump current, this increase was not statistically significant. The ineffectiveness of insulin and phorbol ester may be due to colcemid interfering with Na-K pump translocation from internal vesicles to the sarcolemma. © 1994 wiley-Liss, Inc.     

Multiple driving factors explain spatial and temporal variability in coral calcification rates on the Bermuda platform

Experimental studies have shown that coral calcification rates are dependent on light, nutrients, food availability, temperature, and seawater aragonite saturation (Ω _arag), but the relative importance of each parameter in natural settings remains uncertain. In this study, we applied Calcein fluorescent dyes as time indicators within the skeleton of coral colonies (n = 3) of Porites astreoides and Diploria strigosa at three study sites distributed across the northern Bermuda coral reef platform. We evaluated the correlation between seasonal average growth rates based on coral density and extension rates with average temperature, light, and seawater Ω _arag in an effort to decipher the relative importance of each parameter. The results show significant seasonal differences among coral calcification rates ranging from summer maximums of 243 ± 58 and 274 ± 57 mmol CaCO₃ m^?2 d^?1 to winter minimums of 135 ± 39 and 101 ± 34 mmol CaCO₃ m^?2 d^?1 for P. astreoides and D. strigosa, respectively. We also placed small coral colonies (n = 10) in transparent chambers and measured the instantaneous rate of calcification under light and dark treatments at the same study sites. The results showed that the skeletal growth of D. strigosa and P. astreoides, whether hourly or seasonal, was highly sensitive to Ω _arag. We believe this high sensitivity, however, is misleading, due to covariance between light and Ω _arag, with the former being the strongest driver of calcification variability. For the seasonal data, we assessed the impact that the observed seasonal differences in temperature (4.0 °C), light (5.1 mol photons m^?2 d^?1), and Ω _arag (0.16 units) would have on coral growth rates based on established relationships derived from laboratory studies and found that they could account for approximately 44, 52, and 5 %, respectively, of the observed seasonal change of 81 ± 14 mmol CaCO₃ m^?2 d^?1. Using short-term light and dark incubations, we show how the covariance of light and Ω _arag can lead to the false conclusion that calcification is more sensitive to Ω _arag than it really is.     

Tuning voltage-gated channel activity and cellular excitability with a sphingomyelinase

Voltage-gated ion channels generate action potentials in excitable cells and help set the resting membrane potential in nonexcitable cells like lymphocytes. It has been difficult to investigate what kinds of phospholipids interact with these membrane proteins in their native environments and what functional impacts such interactions create. This problem might be circumvented if we could modify specific lipid types in situ. Using certain voltage-gated K⁺ (K_V) channels heterologously expressed in Xenopus laevis oocytes as a model, our group has shown previously that sphingomyelinase (SMase) D may serve this purpose. SMase D is known to remove the choline group from sphingomyelin, a phospholipid primarily present in the outer leaflet of plasma membranes. This SMase D action lowers the energy required for voltage sensors of a K_V channel to enter the activated state, causing a hyperpolarizing shift of the Q-V and G-V curves and thus activating them at more hyperpolarized potentials. Here, we find that this SMase D effect vanishes after removing most of the voltage-sensor paddle sequence, a finding supporting the notion that SMase D modification of sphingomyelin molecules alters these lipids’ interactions with voltage sensors. Then, using SMase D to probe lipid–channel interactions, we find that SMase D not only similarly stimulates voltage-gated Na⁺ (Na_V) and Ca²⁺ channels but also markedly slows Na_V channel inactivation. However, the latter effect is not observed in tested mammalian cells, an observation highlighting the profound impact of the membrane environment on channel function. Finally, we directly demonstrate that SMase D stimulates both native K_V1.3 in nonexcitable human T lymphocytes at their typical resting membrane potential and native Na_V channels in excitable cells, such that it shifts the action potential threshold in the hyperpolarized direction. These proof-of-concept studies illustrate that the voltage-gated channel activity in both excitable and nonexcitable cells can be tuned by enzymatically modifying lipid head groups.