Voltage and time dependency of calcium mediated phasic and tonic responses in rat vas deferens smooth muscle--the effect of some calcium agonist and antagonist agents

Abstract

1. Phasic and tonic components of the K+-induced contracture response were found to be expressed to different degrees in the prostatic and epididymal portions of the rat vas deferens. 2. With elevation of external potassium greater than 25 mM, the mechanisms underlying the phasic component operate only transiently before inactivation and replacement with tonic tension. 3. Both phasic and tonic components of the vas deferens response to potassium were markedly dependent upon external calcium ions. 4. Nifedipine and verapamil equally inhibited the phasic and tonic components of the K+ response in the prostatic vas deferens. However, inhibition by these agents was far more pronounced in the phasic components than in the tonic component of the epididymal vas deferens. 5. BAY K 8644 potentiated, in a dose-dependent manner, the phasic components of the K+ response, particularly in the prostatic vas deferens. 6. Abscisic acid also potentiated, in a dose-dependent manner the K+ response of rat vas deferens, but this action was far more pronounced in the tonic component of the epididymal portion. 7. Papaverine abolished the BAY K 8644 potentiated epididymal K+ response but did not affect the BAY K 8644 potentiated prostatic K+ response. 8. It is concluded that abscisic acid potentiated responses associated with the activation of voltage-dependent, non-inactivating slow calcium channels. 9. Papaverine, nifedipine and verapamil appear to be less selective than abscisic acid in that they equally inhibit phasic and tonic responses in prostatic vas deferens, but these may be interdependent, yet they more strongly inhibit phasic responses of epididymal vas deferens.