Three components of the calcium current in cultured glomerulosa cells from rat adrenal gland.

Abstract

1. Ca2+ channels were studied in cultured glomerulosa cells from the rat adrenal gland. The whole‐cell configuration of the patch‐clamp technique was used. Cs+‐filled pipettes were used in order to block K+ channels. 2. Three Ca2+ components were found, namely, T, L and N, according to the nomenclature proposed by Nowycky, Fox & Tsien (1985). The T‐component was a fast transient component activated in the range ‐60 to ‐40 mV; the L‐component did not inactivate for a sustained depolarization and activated at voltages around ‐30 mV; the third component, the N‐component, was transient and was activated at voltages close to ‐20 mV. 3. A statistical analysis made on seventy‐one experiments showed that the L‐component was the most frequent (65% of the experiments), followed by the T‐ and finally the N‐ components (59 and 29% of the experiments, respectively). 4. The substitution of Ba2+ ions for Ca2+ ions greatly enhanced the L‐component's amplitude (iBa/iCa = 4) while the N‐component was unaffected and the T‐component was reduced (iBa/iCa = 0.4). 5. A comparison of the voltage‐dependent steady‐state inactivation of the three components showed that the T‐component was inactivated at ‐60 mV while the inactivation of the L‐ and N‐components was complete at ‐25 and 0 mV, respectively. 6. A run‐down effect was detected in some cells. The time stability of the L‐component was lower than that of the T‐component. The N‐component seemed to be insensitive for at least 1 h. The results for the L‐ and T‐components were obtained in cells which presented no run‐down of the current or only a weak one. 7. Cd2+ ions (5 x 10(‐5)M) completely blocked the long‐lasting component (L‐component) and slightly decreased the T‐component. 8. Bay K 8644, a dihydropyridine agonist, enhanced the L‐component at a concentration of 2.5 microM but decreased it for a higher concentration (5 microM). The T‐component was decreased in a reversible way by 1 microM‐Bay K 8644. Nifedipine, a well‐known antagonist, blocked completely the L‐component. This effect was reversed by the addition of Bay K 8644 to the perfusion medium. The T‐component was also blocked by nifedipine, a result which is in keeping with the fact that Bay K 8644 has a weak effect on this current.