Correlation of EGTA and calcium-blocking agents on the response of the bladder to in vitro ischemia

The effects of repetitive field stimulation (model of hyperrelexia) on the responses of isolated strips of rabbit urinary bladder to FS and carbachol were evaluated under a variety of incubation conditions. Compared to contro l conditions, 2 h of repetitive FS in normal, oxygenated Tyrode's solution followed by incubation for 1 h with no stimulation resulted in a 50% decrea se in contractile response to FS and a 30% decrease in the response to carb achol. Incubation in the absence of O-2 and glucose was used as an in vitro model for ischemia. Repetitive stimulation during in vitro ischemia result ed in a significantly greater decrease in the contractile responses to FS a nd carbachol than did in vitro ischemia without repetitive stimulation. The magnitude of contractile dysfunctions in response to both stimuli were sig nificantly reduced in the presence of EGTA (calcium chelator), diltiazem (c alcium channel blocker) or pincidil (potassium channel opener). Incubation with thapsigargin (SR calcium uptake inhibitor) + ryanodine (SR calcium sto rage inhibitor) had no effect. The results of these studies indicate that i nhibition of Ca2+ entry reduces the contractile dysfunctions induced by rep etitive stimulation in the presence of in vitro ischemia. Inhibition of Ca- i(2+) storage and release had no significant effect on the magnitude of con tractile dysfunctions induced by repetitive stimulation an in vitro ischemi a.