Cellular Pathophysiology of Mutant Voltage-Dependent [Ca.sup.2+] Channel CACNA1H in Primary Aldosteronism

The physiological stimulation of aldosterone production in adrenocortical glomerulosa cells by angiotensin II and high plasma [K.sup.+] depends on the depolarization of the cell membrane potential and the subsequent [Ca.sup.2+] influx via voltage-activated [Ca.sup.2+] channels. Germline mutations of the low-voltage activated T-type [Ca.sup.2+] channel CACNA1H (Cav3.2) have been found in patients with primary aldosteronism. Here, we investigated the electrophysiology and [Ca.sup.2+] signaling of adrenal NCI-H295R cells overexpressing CACNA1H wildtype and mutant M1549V in order to understand how mutant CACNA1H alters adrenal cell function. Whole-cell patch-clamp measurements revealed a strong activation of mutant CACNA1H at the resting membrane potential of adrenal cells. Both the expression of wildtype and mutant CACNA1H led to a depolarized membrane potential. In addition, cells expressing mutant CACNA1H developed pronounced action potential--like membrane voltage oscillations. [Ca.sup.2+] measurements showed an increased basal [Ca.sup.2+] activity, an altered [K.sup.+] sensitivity, and abnormal oscillating [Ca.sup.2+] changes in cells with mutant CACNA1H. In addition, removal of extracellular [Na.sup.+] reduced CACNA1H current, voltage oscillations, and [Ca.sup.2+] levels in mutant cells, suggesting a role of the partial [Na.sup.+] conductance of CACNA1H in cellular pathology. In conclusion, the pathogenesis of stimulus-independent aldosterone production in patients with CACNA1H mutations involves several factors: i) a loss of normal control of the membrane potential, ii) an increased [Ca.sup.2+] influx at basal conditions, and iii) alterations in sensitivity to extracellular [K.sup.+] and Na+. Finally, our findings underline the importance of CACNA1H in the control of aldosterone production and support the concept of the glomerulosa cell as an electrical oscillator. Key Words: adrenal gland, primary aldosteronism, voltage-activated T-type calcium channel, CaV3.2, membrane voltage oscillation