Cell proliferation is associated with enhanced capacitative Ca2+entry in human arterial myocytes

Abstract

Depletion of Ca²⁺stores in the sarcoplasmic reticulum (SR) activates extracellular Ca²⁺influx via capacitative Ca²⁺entry (CCE). Here, CCE levels in proliferating and growth-arrested human pulmonary artery smooth muscle cells (PASMCs) were compared by digital imaging fluorescence microscopy. Resting cytosolic free Ca²⁺concentration ([Ca²⁺]_cyt) in proliferating PASMCs was twofold higher than that in growth-arrested cells. Cyclopiazonic acid (CPA; 10 μM), which inhibits SR Ca²⁺-ATPase and depletes inositol 1,4,5-trisphosphate-sensitive Ca²⁺stores, transiently increased [Ca²⁺]_cytin the absence of extracellular Ca²⁺. The addition of 1.8 mM Ca²⁺to the extracellular solution in the presence of CPA induced large increases in [Ca²⁺]_cyt, indicative of CCE. The CPA-induced SR Ca²⁺release in proliferating PASMCs was twofold higher than that in growth-arrested cells, whereas the transient rise of [Ca²⁺]_cytdue to CCE was fivefold greater in proliferating cells. CCE was insensitive to nifedipine but was significantly inhibited by 50 mM K⁺, which reduces the driving force for Ca²⁺influx, and by 0.5 mM Ni²⁺, a putative blocker of store-operated Ca²⁺channels. These data show that augmented CCE is associated with proliferation of human PASMCs and may be involved in stimulating and maintaining cell growth.