Fast axon activity and the motor pattern in cockroach legs during swimming

Abstract Electromyographic recordings were made from muscles that extend the trochanter/femur of each of the six legs of American cockroaches, Periplaneta americana (L.), while the insects swam in water. The recordings showed two novel features. (1) During swimming, muscle activity in different legs was coordinated in the alternating tripod pattern commonly seen during free walking on land, not in the pattern of synchronous leg pairs common to other large terrestrial insects in water. (2) Fast axons were usually recruited along with slow axons, even when the insect swam at a moderate pace. Fast axon activity always started after the middle of the slow axon burst in intact insects, but vanished from most bursts in the stump of the leg after amputation of the femur. The alternating tripod pattern was maintained even after amputation. Possible causes of fast axon recruitment are discussed.     

An ATP-dependent Na/Mg countertransport is the only mechanism for Mg extrusion in squid axons

The components of magnesium efflux in squid axons have been studied under internal dialysis and voltage clamp conditions. The present report rules out the existence of an ATP-dependent, Na₀- and Mg₀-independent Mg²⁺ efflux (ATP-dependent Mg²⁺ pump) leaving the Mg²⁺---Na⁺ exchange system as the only mechanism for Mg²⁺ extrusion. The main features of the Mg²⁺ efflux are: (1) The efflux is completely dependent on ATP. (2) The efflux can be activated either by external Na⁺ (forward Mg²⁺---Na⁺ exchange) or external Mg²⁺ (Mg²⁺---Mg²⁺ exchange). (3) The mobility of the Mg²⁺ exchanger in the Na₀⁺-loaded form is greater than that in the Mg²⁺-loaded one. (4) In variance with the Na⁺---Ca²⁺ exchange mechanism, Mg²⁺---Mg²⁺ exchange is not activated by external monovalent cations. (5) ATPγS replaces ATP in activating Mg²⁺---Na⁺ exchange suggesting that a phosphorylation/dephosphorylation process regulates this transport mechanism.     

Permeability of the squid giant axon to organic cations and small nonelectrolytes

Summary The permeability of the Na channel of squid giant axon to organic cations and small nonelectrolytes was studied. The compounds tested were guanidinium, formamidinium, and¹⁴C-labeled urea, formamide, thiourea, and acetone. Permeability was calculated from measurements of reversal potential and influx on internally perfused, voltage clamped squid axons. The project had two objectives: (1) to determine whether different methods of measuring the permeability of organic cations yield similar values and (2) to see whether neutral analogs of the organic cations can permeate the Na channel. Our results show that the permeability ratio of sodium to a test ion depends upon the ionic composition of the solution used. This finding is consistent with the view put forward previously that the Na channel can contain more than one ion at a time. In addition, we found that the uncharged analogs of permeant cations are not measurably permeant through the Na channel, but instead probably pass through the lipid bilayer.     

precision holding in humans,non-human primates,and Plio-Pleistocene hominids

Human Evolution - Four Types of precision holding in the human hand have been identified and described in accordance with the contrasting regional properties of a differentiated ungual pulp of the...     

On the structure and biological properties of decarbamoylsaxitoxin

The acid hydrolysis product of saxitoxin is shown to be decarbamoylsaxitoxin by spectral characterization and its reconversion to saxitoxin by carbamoylation. Natural and resynthesized saxitoxin are identical in chromatographic and spectral properties and in their potencies in blocking the sodium channel in squid giant axon. The hydrolysis product, decarbamoylsaxitoxin, exhibits 20% of the potency of saxitoxin in the squid axon system. These results confirm the structure of the hydrolysis product and its biological activity relative to saxitoxin.     

Rabbit distal colon epithelium: III. Ca2+-activated K+ channels in basolateral plasma membrane vesicles of surface and crypt cells

Summary In the mammalian distal colon, the surface epithelium is responsible for electrolyte absorption, while the crypts are the site of secretion. This study examines the properties of electrical potential-driven⁸⁶Rb⁺ fluxes through K⁺ channels in basolateral membrane vesicles of surface and crypt cells of the rabbit distal colon epithelium. We show that Ba²⁺-sensitive, Ca²⁺-activated K⁺ channels are present in both surface and crypt cell derived vesicles with half-maximal activation at 5×10^–7 m free Ca²⁺. This suggests an important role of cytoplasmic Ca²⁺ in the regulation of the bidirectional ion fluxes in the colon epithelium.The properties of K⁺ channels in the surface cell membrane fraction differ from those of the channels in the crypt cell derived membranes. The peptide toxin apamin inhibits Ca²⁺-activated K⁺ channels exclusively in surface cell vesicles, while charybdotoxin inhibits predominantely in the crypt cell membrane fraction. Titrations with H⁺ and tetraethylammonium show that both high-and low-sensitive⁸⁶Rb⁺ flux components are present in surface cell vesicles, while the high-sensitive component is absent in the crypt cell membrane fraction. The Ba²⁺-sensitive, Ca²⁺-activated K⁺ channels can be solubilized in CHAPS and reconstituted into phospholipid vesicles. This is an essential step for further characterization of channel properties and for identification of the channel proteins in purification procedures.     

Regulation of Ca2+-activated K+ Channel from Rabbit Distal Colon Epithelium by Phosphorylation and Dephosphorylation

The Ca²⁺-activated maxi K⁺ channel is predominant in the basolateral membrane of the surface cells in the distal colon. It may play a role in the regulation of the aldosterone-stimulated Na⁺ reabsorption from the intestinal lumen. Previous measurements of these basolateral K⁺ channels in planar lipid bilayers and in plasma membrane vesicles have shown a very high sensitivity to Ca²⁺ with a K _0.5 ranging from 20 nm to 300 nm, whereas other studies have a much lower sensitivity to Ca²⁺. To investigate whether this difference could be due to modulation by second messenger systems, the effect of phosphorylation and dephosphorylation was examined. After addition of phosphatase, the K⁺ channels lost their high sensitivity to Ca²⁺, yet they could still be activated by high concentrations of Ca²⁺ (10 μm). Furthermore, the high sensitivity to Ca²⁺ could be restored after phosphorylation catalyzed by a cAMP dependent protein kinase. There was no effect of addition of protein kinase C. In agreement with the involvement of enzymatic processes, lag periods of 30–120 sec for dephosphorylation and of 10–280 sec for phosphorylation were observed. The phosphorylation state of the channel did not influence the single channel conductance. The results demonstrate that the high sensitivity to Ca²⁺ of the maxi K⁺ channel from rabbit distal colon is a property of the phosphorylated form of the channel protein, and that the difference in Ca²⁺ sensitivity between the dephosphorylated and phosphorylated forms of the channel protein is more than one order of magnitude. The variety in Ca²⁺ sensitivities for maxi K⁺ channels from tissue to tissue and from different studies on the same tissue could be due to modification by second messenger systems. Received: 28 February 1995/Revised: 22 December 1995     

The molecular cloning and characterization of potential chick DM-GRASP homologs in zebrafish and mouse

A full-length zebrafish cDNA clone and a partial mouse cDNA clone similar to chick DM-GRASPwere isolated and analyzed. The nucleotide sequence of the full-length zebrafish clone shares 54% identity, and predicts 39% amino acid identity, with chick DM-GRASP. The partial mouse clone shares 76% nucleotide identity, and predicts 76% amino acid identity, with chick DM-GRASP. The predicted proteins encoded by both of these clones exhibit conserved structural domains that are characteristic of the chick protein. These features may identify them as a distinct subfamily within the immunoglobulin superfamily of cell adhesion molecules. Express of the zebrafish DM-GRASP protein is similar to chick DM-GRASP and is principally restricted to a small subset of developing sensory and motor neurons during axonogenesis. Zebrafish DM-GRASP expression was temporally regulated and limited to specific axon domains. This regional expression correlated with fasciculated axon domains. These results suggest that the zebrafish and mouse cDNA clones represent the respective fish and mammalian homologs of thick DM-GRASP. The highly selective expression of zebrafish DM-GRASP suggests that it is involved in the selective fasciculation and guidance of axons along their normal pathways. 1994 John Wiley & Sons, Inc.     

Effect of internal and external K+ on Na+−Ca2+ exchange in dialyzed squid axons under voltage clamp conditions

The effect of external and internal K⁺ on Na_o⁺-dependent Ca²⁺ efflux was studied in dialyzed squid axons under constant membrane potential. With axons clamped at their resting potentials, external K⁺ (up to 70 mM) has no effect on Na⁺?Ca²⁺ exchange. Removal of K_i⁺ causes a marked inhibition in the Na_o⁺-dependent Ca²⁺ efflux component. Internal K⁺ activates the Na⁺?Ca²⁺ exchange with low affinity $\text{(K}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 90 mM)}$. Activation by K_i⁺ is similar in the presence or in the absence of Na_i⁺, thus ruling out a displacement of Na_i⁺ from its inhibitory site. Axons dialyzed with ATP also show a dependency of Ca²⁺ efflux on K_i⁺. The present results demonstrate that K_i⁺ is an important cofactor (partially required) for the proper functioning of the forward Na⁺?Ca²⁺ exchange.