Regional difference in sympathetic neurotransmitter-and Ca 2+ channel-mediated responses in rat vas deferens

Abstract

1. 1. Pharmacological properties were compared in the epididymal and prostatic portions of the rat vas deferens. 2. 2. Contractile response to norepinephrine (NE) was larger in the epididymal portion, in spite of the smaller diameter in this region. In contrast, contraction evoked by ATP or α,β-methylene ATP (α,β-mATP) was larger in the prostatic portion. The sensitivities to NE but not to α,β-mATP are different in these portions. 3. 3. ATP or NE facilitated the contraction induced by the other agonist, suggesting that they cooperatively elicit smooth muscle contraction. This cooperation was observed in both portions. 4. 4. Neither the contraction elicited by the addition of Ca 2+ to smooth muscle depolarized with 63.7 mM extracellular K + nor the relaxation by nifedipine of the depolarized smooth muscle precontracted with 1.8 mM extracellular Ca 2+ was regionally different. However, Bay k 8644 elicited contraction only in the epididymal portion. A combination of 5 mM K + with Bay k 8644 also caused oscillatory contraction in the prostatic portion. 5. 5. A radioligand binding study was performed using the microsomal fraction prepared separately from these portions. Both the dissociation constant and the maximum binding for 3H-nimodipine were smaller in the epididymal fraction than in the prostatic fraction. 6. 6. These results suggest that 1. the NE-elicited contraction is more pronounced in the epididymal portion, 2. the purinoceptor-mediated contractions along the vas deferens are less heterogeneous, and 3. although the sensitivity to Bay k 8644 is higher in the epididymal portion, Ca 2+ channel-mediated responses are not regionally different when they are fully activated.