Calcium channel blocker and calmodulin antagonists affect the gradient of free calcium ions in lily pollen tubes.

The distribution of intracellular free calcium ions ([Ca2+]i) was measured in pollen tubes of Lilium longiflorum using video imaging microscopy and the calcium sensitive indicators fura-2 and quin-2. The mean [Ca2+]i in growing pollen tubes measured with fura-2 shows a maximum of 1.7 to 2.6 microM in the tube tip and decreases almost exponentially to 60 to 100 nM at 100 microns behind the tip. Using quin-2, the maximum [Ca2+]i was also found in the tube tip but with a lower Ca2+ concentration, namely 1 microM. Addition of the calcium channel blocker La3+ caused a decrease of the [Ca2+]i maximum in the tube tip, indicating a heterogeneous distribution of Ca2+ channels along the plasma membrane of pollen tubes. The [Ca2+]i increased after addition of vanadate or compound 48/80. This suggests an involvement of a calmodulin-dependent Ca2+ pump in generation of the Ca2+ gradient in lily pollen tubes. The high [Ca2+]i found in the tube tip with fura-2 seems to indicate the real Ca2+ concentration and is probably responsible for vesicle fusion, fragmentation of actin filaments, and inhibition of cytoplasmic streaming.     

Serum iron, serum ferritin and tissue ferritin during development in ducks

Serum ferritin and tissue ferritin from kidney, heart, small intestine, spleen and liver from ducks during development from 16 to 112 days of age were measured by radioimmunoassay using rabbit anti-duck liver ferritin antibodies and goat second antibody. Serum iron concentration and tissue ferritin iron content are given. Serum ferritin concentration, tissue ferritin and ferritin iron content increase gradually during development. The decrease in all these parameters at 8 weeks of age might be due to molting.     

Therapeutic effects of DCDDP, a calcium channel blocker, on chronic pulmonary hypertension in rat.

To explore the effect of dimethyl 4-(2-chlorophenyl)-1,4-dihydro-2,6-dimethyl-3,5-pyridinedicarboxylate (DCDDP) on pulmonary hypertension (PH) induced by monocrotaline (MCT), the parameters of pulmonary hemodynamics, the contents of endothelin-like immunoreactivity, nitric oxide (NO), malondialdehyde, and superoxide dismutase in plasma and pulmonary homogenate were measured. DCDDP was administered in 5, 50, and 500 microg x kg(-1) x day(-1) ip doses, once a day for 28 days. The antiserotonin effect of DCDDP was investigated by using immunohistochemistry, image analysis, and cell culture technique. The results showed that pulmonary arterial pressure was significantly dropped and pulmonary resistance was decreased in DCDDP groups, compared with the MCT group. DCDDP had no influence on endothelin-like immunoreactivity levels in plasma and pulmonary homogenate but reduced the contents of NO, superoxide dismutase, and malondialdehyde in pulmonary homogenate enhanced by MCT. DCDDP also significantly inhibited the increase in numbers of 5-hydroxytryptamine (5-HT) and 5-HT receptor-positive cells in pulmonary tissue of PH rats induced by MCT. The proliferation and contraction of pulmonary arterial smooth muscle cells and the increase in concentration of free Ca(2+) in them evoked by 5-HT were inhibited significantly by DCDDP. The results suggest that DCDDP reduces the production of free radicals and content of 5-HT and 5-HT receptor and the increase in NO in pulmonary tissue, which underlies the mechanisms of DCDDP against MCT-induced PH.     

The calcium channel blocker verapamil and cancer chemotherapy

Verapamil is an agent which inhibits the transmembrane flux of calcium ions and is used clinically in the management of cardiac arrhythmias. Combination of this calcium antagonist with antineoplastic agents results in the establishment of chemosensitivity in tumor cells resistant to accepted chemotherapeutic agents and, to a lesser degree, potentiates the efficacy of such compounds in drug-sensitive malignancies. Preliminary indications are that the clinical role of such a potentiation of efficacy would not be limited by an increase in generalized toxicity in non-malignant tissues. Data accumulated indicates a verapamil-induced inhibition of the ability of resistant cells to actively extrude chemotherapeutic agents, possibly due to a decrease in calmodulin activity as a result of a drug-induced alteration of the intracellular calcium environment. The results of preclinical trials to date indicate a role for verapamil in augmenting currently accepted chemotherapeutic regimens.     

Bupivacaine is an effective potassium channel blocker in heart

The local anesthetic agent bupivacaine increases action potential duration in isolated frog atrial myocytes, and blocks two potassium conductances, IK and IK1. The effective concentrations, particularly for IK, are similar to those which depress the sodium conductance. Potassium channel block may thus contribute to bupivacaine's reported cardiotoxicity.     

Characterization of ferritin and ferritin-binding proteins in canine serum

Ferritin and ferritin-binding proteins in canine serum were characterized. A certain percentage of ferritin in canine serum, but no tissue ferritin, was precipitated by centrifugation at 16,000×g for 30 min. The precipitated ferritin was found to contain two subunits corresponding to the H and L subunits of canine liver ferritin by immunoblotting, the H subunit being predominant. More ferritin was precipitated from canine sera which had been incubated with anti-rat liver ferritin antibody than from untreated sera, and the H chain also predominated. To evaluate the possibility that the autoantibody was responsible for the precipitation of canine serum ferritin, the ferritin-binding activities of canine antibodies were examined using liver ferritin-coated microtiter plates and alkaline phosphatase-labeled antibodies specific for canine IgM, IgA, and IgG heavy chains. The results showed that IgM and IgA, but not IgG, had considerable ferritin-binding activities. Given these results, we suggest that there is H-chain-rich isoferritin in canine serum, and that ferritin exists as an immune complex.     

Blockade of a KCa channel with synthetic peptides from noxiustoxin: A K+ channel blocker

Using the outside-out configuration of the patch-clamp method, we studied the effect of several synthetic peptides corresponding to various segments from the N-terminal region of noxiustoxin (NTX) on single Ca²⁺-activated K⁺ (K_Ca) channels of small conductance obtained from cultured bovine aortic endothelial cells. These peptides induced diverse degrees of fast blockade in the endothelial K_Ca channel. The most effective blockers were the peptides NTX_1–39 (IC₅₀=0.5 m) and NTX_1–20 comprising the first 20 amino acids from the native toxin (IC₅₀ 5 m), while less effective was the hexapeptide NTX_1–6, from the first six amino acid residues of NTX (IC₅₀ = 500 m). This was the minimum sequence required to block the channel.By testing overlapping sequences from the entire molecule, specially those corresponding to the N-terminal region of NTX, we have been able to determine their different apparent affinities for the K_Ca channel. Synthetic peptides from the C-terminal region produced no effect on the K_Ca channel at the concentrations tested (up to 1 mm). These results confirm that in the N-terminal region of the NTX is located part of the sequence that may recognize K⁺ channels, as we have suggested previously from in vivo experiments. The blockade induced by native NTX was poorly affected by changes in membrane potential; however, the blockage induced by synthetic peptides lacking the C-terminal region was partially released by depolarization.This study was supported by grant HL-45880 from the National Institutes of Health, and by grant 900946 from the American Heart Association to D.L.K. and Howard Hughes Medical Institute No. 75191-527104, CONACyT-Mexico No. 0018-N9105, and DGAPA-UNAM No. IN 202689 to L.D.P. This work was partially supported by a Grant-in-aid No. 92014250 from the American Heart Association to L.V.     

Calcium channel regulation and presynaptic plasticity

Voltage-gated calcium (Ca(2+)) channels initiate release of neurotransmitters at synapses, and regulation of presynaptic Ca(2+) channels has a powerful influence on synaptic strength. Presynaptic Ca(2+) channels form a large signaling complex, which targets synaptic vesicles to Ca(2+) channels for efficient release and mediates Ca(2+) channel regulation. Presynaptic plasticity regulates synaptic function on the timescale of milliseconds to minutes in response to neurotransmitters and the frequency of action potentials. This article reviews the regulation of presynaptic Ca(2+) channels by effectors and regulators of Ca(2+) signaling and describes the emerging evidence for a critical role of Ca(2+) channel regulation in control of neurotransmission and in presynaptic plasticity. Failure of function and regulation of presynaptic Ca(2+) channels leads to migraine, ataxia, and potentially other forms of neurological disease. We propose that presynaptic Ca(2+) channels serve as the regulatory node in a dynamic, multilayered signaling network that exerts short-term control of neurotransmission in response to synaptic activity.     

The course of serum ferritin in blood donors

In the course of 18 months there occurred a decrease in the serum ferritin concentration from 58 +/- 2 micrograms/l to 32 +/- 1 micrograms/l in male donors after 5-6 donations of 400 ml of blood each. Female permanent donors showed a constantly lowered content of an average of 15 +/- 1 micrograms/l. Female first donors attained the serum ferritin level of permanent female donors with the fourth donation, whereas it was not until the fifth donation that male first donors declined to the level of permanent donors. This decrease of serum ferritin content in blood donors points to a depletion of iron stores. This process should be counteracted by exerting an increased influence on nutritional habits supported by oral iron substitution and diminishing the frequency of donation, particularly for female blood donors.     

Calcium channel blockers and behavioral sensitization

Behavioral sensitization to amphetamine-induced stereotypy was previously shown to consist of two separable phenomena, induction and expression, both of which involve the excitatory amino acids (EAA). In the present experiments, the calcium channel blockers (CCB), nifedipine, diltiazem and verapamil, were shown to block both phenomena; these results are similar to those reported earlier for DNQX, an antagonist of the non-N-methyl-D-aspartate receptors for the EAA. The CCB, like DNQX, affect only that percentage of the stereotypic response which results from the sensitization reaction, without affecting the quantitative portion of the response attributable to the acute effect of amphetamine. The results support previous conclusions that the sensitization response consists of two quantitative components, only one of which involves the EAA. The antagonism exhibited by the CCB suggests that behavioral sensitization involves Ca++ and L-type calcium channels.     

Characterization of autoantibodies to ferritin in canine serum

Ferritin-binding proteins circulating in mammalian blood are thought to be involved in the clearance of ferritin. The present study characterizes canine serum autoantibodies (IgM and IgA) that react with ferritin. Canine IgM and IgA bound to bovine spleen ferritin as well as canine liver ferritin. To examine the specificity of canine IgM and IgA to ferritin H and L subunits, we used canine heart ferritin and canine liver ferritin with H/L subunit ratios of 3.69 and 0.43, respectively. Canine IgM and IgA recognized both of the H- and L-subunit-rich isoferritins, showing that their binding activities to ferritin depend on the H-subunit content. Recombinant bovine H-chain ferritin homopolymer expressed in a baculovirus expression system bound more with IgM and IgA than the recombinant L-chain homopolymer expressed under the same conditions. These results suggest that canine IgM and IgA recognize H-subunit-rich isoferritins, and that H-subunit-rich isoferritins are cleared from the circulation more rapidly than L-subunit-rich isoferritins.     

Lipoprotein and protein binding of the calcium channel blocker diltiazem

The plasma protein binding properties of the calcium channel blocker diltiazem were studied using a three-chamber equilibrium dialysis system. Diltiazem is 81% bound to human sera with significant inter-individual variation. The relative binding of diltiazem by lipoproteins and alpha 1-acid glycoprotein was higher than by albumin. The binding to low density lipoprotein was strong and appeared not to be associated with the surface apoprotein.