Simultaneous registration of Ca(2+) transients and volume changes in rat mesangial cells: Evaluation of the effects of protein kinase C down-regulation.

The intracellular free Ca(2+) concentration ([Ca(2+)]i) could be correlated with the contractile response in rat mesangial cells using an apparatus which measured both biochemical processes simultaneously. Long-term pretreatment of mesangial cells with 12-O-tetradecanoly-phorbol 13-acetate (24 h, 500 nM) increased the (20 nM) angiotensin II-induced mobilization of Ca(2+) and led to an enhanced and sustained contraction of the cells. The contractile response was delayed by approximately 3.5 s with respect to the intracellular increase in Ca(2+) concentration. The simultaneous registration of Ca(2+) transients and cell contractions confirms that [Ca(2+)]i is the major determinant of the angiotensin II-mediated mesangial cell contraction.