The contribution of intracellular Ca2+ release to contraction in human bladder smooth muscle.
1. The importance of Ca2+ release from the sarcoplasmic reticulum (SR) in excitation contraction (EC) coupling in human detrusor muscle remains controversial. In this paper the contribution of Ca2+ release to agonist induced contraction is assessed. 2. Dose response curves to carbachol (0.01 - 10 microM) were constructed before and after exposure to 200 nM Thapsigargin (Tg). Tg pre-treatment reduced the force of contraction at all agonist concentrations however, the reduction was dose dependent. At 0.1 microM the contractions were reduced to 14.5 +/- 7% (mean +/- s.e.mean) of controls (n = 8) while at 10 microM the contractions were only reduced to 92 +/- 3% of controls (n = 10). 3. The role of external Ca2+ was examined by measuring the magnitude of contraction to low and high doses of agonist in the presence and absence of external Ca2+. With (0.1-0.3 microM) carbachol the contractions in nominally Ca2+ free media were 4+/-4% of controls (n = 7) whilst with (1 - 10 microM) carbachol the contractions were 36 +/- 8% of controls (n=7) suggesting that at low agonist concentrations the release of Ca2+ has a requirement for external Ca2+. 4. Pre-treatment of muscle strips with the Ca2+ channel blocking agent diltiazem reduced the contractile responses to carbachol. Contractions induced by 0.1 microM were reduced to 29+/-11% (P<0.05) of controls while those activated by 10 microM were reduced to 86+/-6% (P= 0.1) of controls (n = 4) suggesting the Ca2+ influx needed to activate internal store release at low agonist stimulation is through L-type Ca2+ channels. 5. These observations confirm the importance of thapsigargin sensitive intracellular Ca2+ store release in the activation of contraction of detrusor smooth muscle and suggest the overall contribution of this store depends upon the magnitude of the agonist stimulation.
Masters
J G
JG
Department of Surgical Sciences, The School of Surgical and Reproductive Sciences, The Medical School, University of Newcastle upon Tyne.
Neal
D E
DE
Gillespie
J I
JI
D002118:Calcium / Q000378:metabolism*; D002217:Carbachol / Q000494:pharmacology; D004110:Diltiazem / Q000494:pharmacology; D006801:Humans; D066298:In Vitro Techniques; D009119:Muscle Contraction / Q000187:drug effects*; D019284:Thapsigargin / Q000494:pharmacology; D001743:Urinary Bladder / Q000187:drug effects / Q000502:physiology*
D019284:Thapsigargin; D002217:Carbachol; D004110:Diltiazem; D002118:Calcium