Series Of Ca2 Research Articles

Increase in intracellular calcium ions upon fertilization in animal eggs.

A transient rise in the concentration of Ca2+ in the cortex upon ferttilization was demonstrated in echinoderm, teleost, amphlian and mammalian eggs by the luminescence of aequorin which had been microinjected into the egg, with a high sensitivity video-microscopic system. The Ca2+ increase started near the site of sperm entry and was propagated as a wave along the cortex toward the antipode of the egg. The wave occurred once and the propagation velocity of the wave was about 10μn/sec in echinoderm, teleost and amphibian eggs at room temperatures, while a series of Ca2+ waves with a higher propagation velocity were observed in golden hamster eggs in a warmed condition. Possible involvement of Ca2+ and inositol 1, 4, 5-triphosphate in the activation upon fertilization was investigated.

Axonal contribution to subthreshold currents inaplysia bursting pacemaker neurons

The contribution of axonal activity to the ionic currents which generate bursting pacemaker activity was studied by using the two-electrode voltage-clamp technique in Aplysia bursting neuron somata in conjunction with intraaxonal voltage recordings. Depolarizing voltage-clamp pulses applied to bursting cell somata triggered axonal action potentials. The voltage-clamp current recording exhibited transient inward current "notches" corresponding to each of the axonal spikes. The addition of 50 microM tetrodotoxin (TTX) to the bathing medium blocked the fast axonal spikes and current notches, revealing a slower axonal spike which was blocked by the replacement of external Ca2+ with Co2+. The inward current evoked by applying a depolarizing voltage-clamp pulse in the soma is distorted by the occurrence of the axonal Ca2+ spike. Elimination of the axonal spike, by injecting hyperpolarizing current into the axon, changes both the time course and the magnitude of the inward current. The axonal Ca2+ spikes are followed by a series of Ca2+-dependent afterpotentials: a rapid postspike hyperpolarization, a depolarizing afterpotential (DAP) and, finally, a long-lasting postburst hyperpolarization. The long-lasting hyperpolarization is not blocked by 50 mM external tetraethyl ammonium, an effective blocker of Ca2+-activated K+ current [IK(Ca)], and does not appear to reverse at EK. Hence, the axonal long-lasting hyperpolarization may not be due to IK(Ca). Somatic voltage-clamp pulses in bursting neurons are followed by a slow inward tail current, which is sometimes coincident with a DAP in the axon. In some cells, the amplitude of the slow inward tail current is greatly reduced if axonal spikes and DAPs are prevented by hyperpolarization of the axon, while, in other cells, elimination of axonal activity has little effect. Therefore, the slow inward tail current is not necessarily an artifact of poor voltage-clamp control over the axonal membrane potential but probably results from the activation of an ionic conductance mechanism located partly in the axon and partly in the soma.

Periodic increase of cytoplasmic free calcium in fertilized hamster eggs measured with calcium‐sensitive electrodes.

The hamster egg at fertilization shows transient, periodic hyperpolarizing responses due to a Ca2+-activated K+ conductance. The suggested increase of the intracellular Ca2+ concentration ([Ca2+]i) was measured with Ca2+-sensitive microelectrodes in combination with the voltage-clamp technique. Calculated values of the basal [Ca2+]i before fertilization averaged in the range 0.2-0.4 microM. Insemination of eggs induced periodic Ca2+ transients with exact one-to-one correspondence to periodic, Ca2+-activated K+ currents. They were recorded anywhere in the cytoplasm, even far from the site of sperm-egg fusion, indicating that [Ca2+]i increases in the whole egg upon each response. During a series of responses after insemination the increase in [Ca2+]i reached 1-2 microM in the first three responses and the peak value decreased to 0.7-0.8 microM in the later responses. The rise and decay times of each Ca2+ transient were 6.8 +/- 2.8 and 22 +/- 6 s (mean +/- S.D., n = 36), respectively. No significant difference in the amplitude and time course of the Ca2+ transient was detected in relation to the depth of the cytoplasm about 3-30 micron from the surface. The basal [Ca2+]i increased gradually from 0.39 to 0.56 microM (average in fourteen eggs) during the series of Ca2+ transients. The biological significance and mechanism of the periodic increase in [Ca2+]i and the response time of the Ca2+ electrode are discussed.

Inhibitory actions of a series of Ca2+ channel antagonists against agonist and K+ depolarization induced responses in smooth muscle: an assessment of selectivity of action

The inhibitory effects of the Ca2+ channel antagonists D-600, diltiazem, nifedipine and seven 1,4-dihydropyridine analogs of nifedipine against 80 mM K+ depolarization induced responses in guinea pig trachea, parenchyma, and pulmonary artery and rat renal and mesenteric artery preparations were determined. Together with similar data previously obtained for guinea pig ileum and bladder, these data permitted an assessment of tissue selectivity of action in smooth muscles of a series of Ca2+ channel antagonists under constant conditions (saline composition) and an identical challenge (K+ depolarization). Very similar rank orders of activity were expressed in all tissues suggesting that the same basic structure-activity relationship operates. However, the series of antagonists were significantly less active in respiratory smooth muscle than in other visceral or vascular smooth muscles. pA2 values for a series of 1,4-dihydropyridine antagonists measured in guinea pig taenia coli against Ca2+-induced responses in K+-depolarizing media correlated with mean inhibitory concentration values against K+-induced responses, suggesting that the latter were an appropriate measure of antagonist potency. pA2 values measured for nifedipine, D-600, and diltiazem against Ca2+-induced responses in taenia coli in the presence of a depolarizing K+ saline, or methylfurmethide, histamine, or 5-hydroxytryptamine did not differ, suggesting that the same channels were activated regardless of stimulant.