Adrenal fasciculata cells express T-type and rapidly and slowly activating L-type Ca channels that regulate cortisol secretion

Enyeart JJ, Enyeart JA. Adrenal fasciculata cells express T-type and rapidly and slowly activating L-type Ca channels that regulate cortisol secretion. Am J Physiol Cell Physiol 308: C899–C918, 2015. First published March 18, 2015; doi:10.1152/ajpcell.00002.2015.—In whole cell patch-clamp recordings, we characterized the L-type Ca currents in bovine adrenal zona fasciculata (AZF) cells and explored their role, along with the role of T-type channels, in ACTHand angiotensin II (ANG II)-stimulated cortisol secretion. Two distinct dihydropyridine-sensitive L-type currents were identified, both of which were activated at relatively hyperpolarized potentials. One activated with rapid kinetics and, in conjunction with Northern blotting and PCR, was determined to be Cav1.3. The other, expressed in approximately one-half of AZF cells, activated with extremely slow voltage-dependent kinetics and combined properties not previously reported for an L-type Ca channel. The T-type Ca channel antagonist 3,5-dichloro-N-[1-(2,2-dimethyl-tetrahydro-pyran-4ylmethyl)-4-fluoro-piperidin-4-ylmethyl]-benzamide (TTA-P2) inhibited Cav3.2 current in these cells, as well as ACTHand ANG II-stimulated cortisol secretion, at concentrations that did not affect L-type currents. In contrast, nifedipine specifically inhibited L-type currents and cortisol secretion, but less effectively than TTA-P2. Diphenylbutylpiperidine Ca antagonists, including pimozide, penfluridol, and fluspirilene, and the dihydropyridine niguldipine blocked Cav3.2 and L-type currents and inhibited ACTH-stimulated cortisol secretion with similar potency. This study shows that bovine AZF cells express three Ca channels, the voltage-dependent gating and kinetics of which could orchestrate complex mechanisms linking peptide hormone receptors to cortisol secretion through action potentials or sustained depolarization. The function of the novel, slowly activating L-type channel is of particular interest in this respect. Regardless, the well-correlated selective inhibition of Tand L-type currents and ACTHand ANG II-stimulated cortisol secretion by TTA-P2 and nifedipine establish the critical importance of these channels in AZF cell physiology.