Effect of potassium on the contractile response of the rat detrusor muscle to field stimulation at increasing calcium concentrations

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1. At 0.6 and 1.8 mM calcium, increasing the potassium concentration from 2.5 to both 7.5 and 12.5 mM significantly increased the contractile response to field stimulation at 0.5, 1, 2 and 4 Hz. There were no effects on the contractile responses to 8, 16, 32 and 64 Hz. 22.5 mM potassium significantly reduced the contractile response to all frequencies of stimulation. 2. At 5.4 mM calcium, the contractile responses to all frequencies in the presence of 2.5, 7.5 and 12.5 mM potassium were similar. The responses to all frequencies of stimulation in the presence of 22.5 mM potassium were significantly reduced. 3. In general, the relative responses to low frequencies of stimulation were significantly greater in the presence of 5.4 mM calcium than in the presence of 0.6 or 1.8 mM calcium. 4. The magnitude of the inhibition in the presence of 22.5 mM potassium was inversely proportional to the extracellular calcium concentration, i.e. the lower the calcium concentration, the greater the inhibition. 5. The bladder base responded to alterations in the potassium and calcium concentrations similarly to the bladder body. 6. In conclusion, increasing the potassium concentration from 2.5 mM (normal bath concentration) to 7.5 and 12.5 mM significantly enhanced the contractile response to low frequency stimulation at both 0.6 and 1.8 mM (normal bath concentration) calcium.

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