The low voltage-activated (T-type) Ca²⁺ channel has been implicated in the regulation of aldosterone secretion from the adrenal zona glomerulosa by extracellular K⁺ levels, angiotensin II, and ACTH. However, the identity of the specific subtype mediating this regulation has not been determined. We utilized in situ hybridization to examine the distribution of three newly cloned members of the T-type Ca²⁺ channel family, α_1G, α_1H, and α_1I, in the rat and bovine adrenal gland. Substantial expression of only the mRNA transcript for the α_1H-subunit was detected in the zona glomerulosa of both rat and bovine. A much weaker expression signal was detected for the α_1H transcript in the zona fasciculata of bovine. Whole cell recordings of isolated bovine adrenal zona glomerulosa cells showed the native low voltage-activated current to be inhibited by NiCl₂ with an IC₅₀ of 6.4 ± 0.2 μM. Because the α_1H subtype exhibits similar NiCl₂ sensitivity, we propose that the α_1Hsubtype is the predominant T-type Ca²⁺ channel present in the adrenal zona glomerulosa.