SUMMARY1. Two types of voltage-sensitive calcium channels were identified and studied in the neuroblastoma cell line NIE-115. Calcium channel currents as carried by Ba2+ (50 mM) were recorded using the whole-cell variation of the patch-electrode voltageclamp technique.2. A transient (type I) inward Ba2+ current was evoked by a step depolarization from a holding potential of -80 mV to potentials more positive than -50 mV. The current amplitude became maximum around -20 mV.3. A depolarization to potentials more positive than -20 mV evoked a long-lasting (type II) component of the inward Ba2+ current. This component reached its maximum around + 10 mV and did not inactivate during a prolonged depolarizing pulse lasting 400 ms.4. When preceded by a 5 s conditioning pulse to -30 mV, step depolarization failed to evoke a transient current due to inactivation. However, it induced a long-lasting current.5. A transient current isolated as the component sensitive to conditioning depolarization became faster in its time course and smaller in its amplitude with membrane depolarization. The current direction was still inward at + 60 mV.6. From the differential voltage sensitivity and the independent channel activity described above, calcium channels responsible for the transient current (type I channel) and those responsible for the long-lasting current (type II channel) were considered to be two different entities.7. Cd2+ preferentially blocked type II channels, whereas La3+ was a highly potent blocker for both types of calcium channels.8. The relative potency for block by polyvalent cations was as follows (apparent dissociation constant in /LM): La3+, 15 > Ni2+, 47 > Cd2+, 160 = Co2+, 160 for type I channels, and La3+, 0 9 > Cd2+, 7 0 > Ni2+, 280 > Co2+, 560 for type II channels.9. The two types of calcium channels were equally sensitive to the temperature. The current amplitude was reduced by cooling below 30 'C. The temperature coefficient (Q10) value was estimated to be 3-0 between 20 and 30 0C, and 15-0 below 20 'C. Above 30 'C, warming reduced the amplitude slightly.

SUMMARY1. Threshold changes of Na and Ca currents due to various polyvalent cations (stabilizing cations) or H+ ions were studied in the egg cell membrane of a tunicate, Halocynthia roretzi, by using the voltage-clamp technique.2. With an increase in [Ca], or a decrease in pH in the external solution, the current-voltage (I-V) relations for the peak of the Na and Ca currents shifted along the voltage axis in the positive direction. These voltage shifts in the I-V relations, measured at a potential of Vi where inward current attains its half-maximum, were shown to be identical to shifts in voltage-dependence of the time courses of Na and Ca currents, and also identical to shifts in the inactivation curves of Na current along the voltage axis.3. The shifts in Vi produced by various polyvalent cations or H+ ions were analysed by the Gouy-Chapman equation for the diffuse double layer, by assuming that a change in Vi directly corresponds to a change in the surface double layer potential.4. The V.-divalent cation concentration relations of Na current were exactly described by the predictions of the theory with a constant value of the surface charge density of le-/(9 A)2.

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SUMMARY1. The effects of alterations of the intracellular ionic composition on the properties of anomalous (or inward) rectification of the egg membrane of the starfish, Mediaster aequalis, were studied by using an intracellular perfusion technique. The following results were obtained, analyzing the membrane current with the voltage-clamp technique.2. The inward rectification of the K conductance depends only on the membrane potential, V, when the K equilibrium potential, VK, is altered by changing the internal K+ concentration at a fixed external K+ concentration, while it depends on V -VK when VK is altered by changing the external K+ at a fixed internal K+ concentration.3. From the above the conclusion is reached that the gating of the K channel of the inward rectification depends on V and external but not internal K+ concentration.4. The conductance of the K channel at a given voltage is roughly proportional to the square root of [K+]1 when the latter is altered at a fixed external K+ concentration.5. Since the conductance is proportional to the square root of [K+]o when this is altered at a fixed internal K+ concentration, the final conclusion is that this conductance is proportional to the geometric mean of the external and internal K+ concentrations. 6. Intracellular Na+ ions are necessary for the activation of inward rectification; the K conductance increases sharply with internal Na+ concentration, reaching saturation at 200 mM. 7. A similar potentiating effect is found for Li+, although it is weaker. Rb+, Cs+ and organic cations such as arginine+ do not have this effect.

Leucine-enkephalin, methionine-enkephalin, and morphine caused a reversible block of Ca21 channel currents in neuroblastoma-glioma hybrid cells (NG108-15