Partially purified Grammostola spatulata venom inhibits stretch activated calcium signaling in bladder myocytes and improves bladder compliance in an in vitro rat whole bladder model.

Abstract

Stretch activated nonselective cationic channels (SACs) are present in urinary bladder myocytes and thought to be activated during bladder filling. We investigated the relationship of stretch induced calcium signaling inhibition in bladder myocytes and bladder compliance modulation in an in vitro whole bladder model. Grammostola spatulata venom (SpiderPharm, Yarnell, Arizona) was purified by preparative high performance liquid chromatography. The resulting fractions were examined for their ability to inhibit the swelling activated intracellular free Ca2+ signal in cultured bladder myocytes. An in vitro rat whole bladder model was used to examine the effect of venom fractions on compliance, emptying and spontaneous contractions during bladder filling. The gadolinium ion, a SAC inhibitor, and venom fractions caused concentration dependent inhibition of the swelling activated intracellular free Ca2+ signal in bladder myocytes. When tested in a rat isolated whole bladder model, 0.1 and 0.2 mg./ml. partially purified venom produced a significant improvement in compliance (p <0.05), caused significant inhibition of the frequency of spontaneous bladder contractions (mean +/- SEM 35.8% +/- 3.7% and 62.3% +/- 4.4%, respectively, p </=0.001) and significantly reduced spontaneous bladder emptying, that is emptying in the absence of exogenous stimulation (38.8% +/- 5.6% and 43.9% +/- 2.5%, respectively, p </=0.0008). However, it produced little or no inhibition of carbachol induced bladder emptying. Our data suggest that the activation of stretch induced signaling in bladder myocytes may have an important role in myogenic regulation of bladder contractility during bladder filling. Inhibition of SACs may improve bladder compliance.