Voltage-dependent calcium currents in dissociated granule cells from rat cerebellum

Voltage-dependent calcium currents were investigated by the patch-clamp technique in whole-cell recording configuration in cultures from 8-day-old rat cerebella, which contained >=90% granule cells. In solutions designed to minimize the sodium and potassium conductances and in 20 mM barium, an inward current activated around -25 mV, reached a peak amplitude at +20 mV and reversed around +80 mV. In 20 mM calcium, this current was ?50% of that in barium. From one to three days in vitro only 16% of the cells tested (n = 20) had a current exceeding 50 pA in maximum amplitude, while after four days in vitro the current reached 100 pA in all neurons tested (n > 70). Verapamil (50-100 ?M) reversibly depressed this current. The dihydropyridine agonist Bay K 8644 (1 ?M) enhanced the maximum conductance by 25 ± 8% (n = 4), caused a negative shift in the activation of 21 ± 5mV and a prolongation of the deactivation time course as the voltage was stepped back from +20 to -80 mV. The GABAB agonist baclofen (50 ?M) reversibly depressed the current by 27 ± 8% in 80% of the cells. The effect was similar to that of GABA and (10 ?M), when the GABAA response (chloride current) was partially blocked by bicucculine. This current can be classified as a dihydropyridine-sensitive high-voltage-activated calcium current. The modulation by GABAB agonists is likely to be significant for presynaptic inhibition.