Role of Intracellular Ca++ in Contraction and Relaxation of Rabbit Corpus Cavernosal Smooth Muscle

Seo, Seong Il; Choi, Woong Ki; Kim, Joon Chul; Yoon, Jai Young; Hwang, Tae Kon; Park, Young Hyun

Abstract

PURPOSE: To elucidate the role of intracellular Ca++ stores in rabbit corpus cavernosal tissue, we performed organ bath study using strips from rabbit corpus cavernosum.
MATERIALS AND METHODS
The corpus cavernosal strips of New Zealand white rabbit (3.0-3.5kg) were mounted in organ chambers to measure isometric tension. Each rabbit corporal strips of 3x10mm in size was incubated for 12 hours to reduce spontaneous contractions. The effects of Ca++ free Tyrode solution and TMB-8 (intracellular Ca++ blocker) on electrically and adrenergically induced contractions were evaluated. And the effects of ATP, bethanechol, sodium nitroprusside(SNP) and electrical stimulation(ES) in the presence of phenylephrine(PE) prestimulation were determined prior to and following preincubation with TMB-8. The responses were monitored via an FT03 force transducer and recorded on a Grass 7D polygraph and expressed as the g tension per 100mg of tissue in contractile response and percent of maximum contraction in relaxation response.
RESULTS
PE and ES induced contractions were reduced depending on time but were not disappeared in the Ca++ free solution after 30minutes. Preincubation for 15minutes with 20uM TMB-8 significantly reduced contractile response of corporal smooth muscle (p<0.05). Relaxation responses to bethanechol and ES in TMB-8 preincubated group were significantly reduced in comparison with non-preincubated group (p<0.05). But there is no statistical differences between responses to ATP and SNP in TMB-8 preincubated and non-preincubated group.
CONCLUSIONS
PE and ES induced contraction and NO mediated relaxation(bethanechol, ES) of corporal smooth muscle depend, in part, on the bioavailability of intracellular Ca++ via release through TMB-8 sensitive channels.