Vasopressin increases cytosolic free calcium concentration in glomerular mesangial cells

Cytosolic free calcium concentration ([Ca²⁺](f)) was determined in cultured rat glomerular mesangial cells under basal conditions and after exposure to arginine vasopressin (AVP) or angiotensin II (ANG II). [Ca²⁺](f) was determined using quin 2 or fura-2, two intracellular fluorescent probes. [Ca²⁺](f) was measured to be 102 ± 3 nM (n=154) using quin 2 and 82 ± 4 (n=34) using fura-2. AVP and ANG II increased [Ca²⁺](f). Maximal levels of [Ca²⁺](f) were achieved in <10 s after addition of the hormone. This peak value was followed by a rapid fall toward the base line. With fura-2 as the intracellular Ca²⁺ indicator, [Ca²⁺](f) increased from 74 ± 7 to a peak of 578 ± 39 nM (n=17) with 100 nM AVP. At 115 s after addition of AVP, [Ca²⁺](f) was 125 ± 9 nM. Similar peak levels of [Ca²⁺](f) were observed using quin 2. The increase in [Ca²⁺](f) was due in large part to release of Ca²⁺ from intracellular stores, since reduction in extracellular free [Ca²⁺] with EGTA did not prevent the hormone-induced increase in [Ca²⁺](f), although it did result in a decreased peak level and a more rapid return to the base line. The AVP-induced increase in [Ca²⁺](f) was blocked by the V₁ receptor antagonist (CH₂)₅Tyr(Me)V(D)AVP. Neither isoproterenol, which increased adenylate cyclase activity, nor dibutyryl cAMP had any affect on [Ca²⁺](f) directly or on the AVP-induced increase in [Ca²⁺](f). In this report we present the first direct measurements of [Ca²⁺](f) and hormone-induced changes in [Ca²⁺](f) in glomerular mesangial cells. We conclude that AVP increased [Ca²⁺](f) by interaction with a cellular V₁ receptor with subsequent mobilization of intracellular Ca²⁺ stores. This increase in [Ca²⁺](f) is likely an intracellular mediator of AVP-induced contraction and prostaglandin production in the mesangial cell.