Contraction of Cultured Rat Glomerular Cells ofApparent

electron microscopy. Relaxation recurred 15 min after hormonal addition at 23°C. Similar experiments in cloned rat glomerular epithelial cells or "renin"producing cells did not demonstrate a contractile response. The contraction of MS cells was independent ofcyclic AMP (cAMP) and cyclic 3',5'-guanosine monophosphate (cGMP) production, even when cyclic nucleotides were measured as early as 30 s after hormonal stimulation. To demonstrate that contraction was a function of hormone-receptor interaction, binding of [3H](8lysine)vasopressin was studied. Specific binding for 1.6 and 5 nM hormone was both timeand dose-dependent. The estimated apparent affiniity was 10 nM. In late MS cell passages (>16th) that no longer demonstrated hormone-stimulated contraction, no specific binding of [3H](8-lysine)vasopressin was observed. Incubations were modified to optimize the conditions for detecting the effect of hormones on cell cyclic nucleotide content. A supramaximal concentration of AVP (200 nM) increased the cAMP content of MS cells twofold in the presence of a phosphodiesterase inA preliminary report of this work was presented at the Annual Meeting of the American Society of Nephrology, November 1979, Boston, Mass. Dr. Roy's present address is Laboratoire de Physiologie Cellulaire, College de France, Paris, France. Received for publication 16 August 1979 and in revised form 5 November 1979. 754 hibitor. Similar experiments with prostaglandin E2 (1 ,ug/ml) led to a 1.5-6-fold increase in MS cell cAMP content, but no effect on contraction was observed. Neither hormone altered cGMP content. These data are further support for the independence of contraction and cyclic nucleotide production. Our studies suggest that MS cells are the equivalent of smooth muscle cells in the glomerulus and that their contraction may be important in control of glomerular filtration.