REGIONAL DIFFERENCES IN THE CONTRACTILE AND INTRACELLULAR CA2-PIG VAS-DEFERENS TO NEUROTRANSMITTERS AND EXCESS K+( RESPONSES OF THE GUINEA)

The contractile responses to various concentrations of noradrenaline ( NA), adenosine triphosphate (ATP), acetylcholine (ACh) and excess exte rnal K+ in the epididymal, middle and prostatic portions of the guinea -pig vas deferens were investigated by measuring the isotonic contract ion, and the intracellular Ca2+ concentration ([Ca2+](i)) using fura-2 fluorescence. In the epididymal portion, the contractions evoked by e ach of these agonists were biphasic, comprising a transient followed b y a tonic phase. In the middle portion, NA and ACh evoked biphasic con tractions, whereas the ATP-induced contraction was an almost monophasi c transient. In contrast, in the prostatic portion, only transient con tractions were evoked by ACh and ATP, while the NA-induced contraction was oscillatory. The responses to each of the neurotransmitters in th e three portions were not affected by pretreatment with TTX. The maxim al responses of tonic contraction in reponse to each of the neurotrans mitters were largest in the epididymal portion, decreased in the middl e and were almost absent in the prostatic portion. These regional diff erences in the contractile properties of the vas deferens were also ev ident upon stimulation with excess external K+. As with the contractil e responses, regional differences in the [Ca2+](i) increases were obse rved during exposure to all the stimulants. It is suggested that the r egional differences in the contractile responses of the vas deferens t o various neurotransmitters and excess external K+ may involve variati on in the mechanisms of Ca2+ homeostasis and in the sensitivity of the contractile apparatus to intracellular Ca2+ ions.