Abstract: | A two-microelectrode voltage-clamp method was used to measure a high-threshold calcium current (ICa) on isolated snail neurons. Tolbutamide (1–5 mmole/liter) and H-8 (1–30 µmole/liter), inhibitors of kinase A, caused a decrease in the peak amplitude and accelerated ICa decay during a depolarizing stimulus. The half-life of the "slow" time constant of ICa decay decreased in the presence of tolbutamide, and was two to three times stronger than the half-life of the "fast" time constant. ICa inactivation curves plotted in a double-stimulus experiment have shown that after tolbutamide application, ICa inactivation elicited by the application of high-amplitude depolarizing pre-stimuli preferentially rises (Vc=+30 to +70 mV). The results suggest that dephosphorylation of Ca2+ channels enhances a potential-dependent component of the inactivation process.Scientific-Research Institute of the Brain, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 23, No. 5, pp. 515–519, September–October, 1991. |