A role for T-type Ca2+ channels in the synergistic control of aldosterone production by ANG II and K+.
Independently, plasma K+ and ANG II stimulate aldosterone secretion from adrenal glomerulosa (AG) cells, but together they synergistically control production. We studied mechanisms to mediate this synergy using bovine AG cells studied under physiological conditions (in 1.25 mM Ca2+ at 37 degrees C). Increasing K+ from 2 to 5 mM caused a potentiation of ANG II-induced aldosterone secretion and a substantial membrane depolarization ( approximately 21 mV). ANG II inhibited a K+-selective conductance in both 2 and 5 mM K+ but caused only a slight depolarization because, under both conditions, membrane potential was close to the reversal potential of the ANG II-induced current. ANG II activated calcium/calmodulin-dependent protein kinase II (CaMKII) equivalently in 2 and 5 mM K+. However, CaMKII activation caused a hyperpolarizing shift in the activation of T-type Ca2+ channels, such that substantially more current was elicited at membrane potentials established by 5 mM K+. We propose that synergy in aldosterone secretion results from K+-induced depolarization and ANG II-induced modulation of T-type channel activation, such that together they promote enhanced steady-state Ca2+ flux.
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000450:Aldosterone / Q000096:biosynthesis* / Q000378:metabolism; D000804:Angiotensin II / Q000494:pharmacology*; D000818:Animals; D015220:Calcium Channels / Q000502:physiology*; D020747:Calcium Channels, T-Type; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D002417:Cattle; D004357:Drug Synergism; D006160:Guanosine Triphosphate / Q000494:pharmacology; D066298:In Vitro Techniques; D015640:Ion Channel Gating / Q000502:physiology; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000494:pharmacology*; D015221:Potassium Channels / Q000502:physiology; D015384:Zona Glomerulosa / Q000737:chemistry / Q000187:drug effects / Q000201:enzymology*