REGULATION OF HORMONE-SENSITIVE CALCIUM INFLUX BY THE ADENYLYL-CYCLASE SYSTEM IN RENAL EPITHELIAL-CELLS

To study signaling pathways regulated by alpha(s) and alpha(i1) in renal epithelial cells, we expressed mutant, activated forms of alpha(s) and alpha(i1) in a continuous proximal tubule cell line (MCT cells). alpha(sQ227L) increased cAMP production, and alpha(ilQ204L) reduced forskolin-sensitive cAMP production. alpha(ilQ204L) increased and alpha(sQ227L) decreased bradykinin-induced Ca influx across the cell membrane, but neither mutant affected bradykinin-stimulated intracellular Ca release or basal Ca influx. BradSkinin-stimulated Ca influx was reduced by dibutyryl cAMP, isoproterenol, and forskolin. Expression of a mutant regulatory type I subunit for cAMP-dependent protein kinase with reduced affinity for cAMP and treatment with KT-5720, a specific cAMP-dependent protein kinase inhibitor, enhanced Ca influx to a degree similar to that in cells expressing alpha(ilQ204L) Bradykinin-stimulated c-fos mRNA expression is partially dependent on extracellular Ca. alpha(sQ227L) reduced and alpha(ilQ204L) enhanced bradykinin-stimulated c-fos expression Consequently, in bradykinin-stimulated cells, the adenylyl cyclase system regulates Ca influx through cAMP-dependent protein kinase, but not intracellular Ca release. Furthermore, the Ca influx mechanism acts as an integrator of two signaling pathways such that Ca-dependent signals are damped by activators of adenylyl cyclase and enhanced by inhibitors of adenylyl cyclase.