Absence of force suppression in rabbit bladder correlates with low expression of heat shock protein 20.
BACKGROUND
Nitroglycerin can induce relaxation of swine carotid artery without sustained reductions in [Ca2+]i or myosin regulatory light chain (MRLC) phosphorylation. This has been termed force suppression and been found to correlate with ser16-phosphorylation of heat shock protein 20 (HSP20). We tested for the existence of this mechanism in a smooth muscle that is not responsive to nitric oxide.


METHODS
Isometrically mounted mucosa free rabbit bladder strips were contracted with carbachol and relaxed with 8-Br-cGMP, forskolin, or isoprenaline.


RESULTS
Contraction was associated with a highly cooperative relation between MRLC phosphorylation and force such that very small increases in MRLC phosphorylation induced large increases in force. Relaxation induced by 8-Br-cGMP, forskolin, or isoprenaline did not shift the MRLC phosphorylation-force relation from that observed with carbachol alone, i.e. there was no force suppression. HSP20 content was negligible (approximately two hundred-fold less than swine carotid).


CONCLUSIONS
The lack of force suppression in the absence of HSP20 is consistent with the hypothesized role for HSP20 in the force suppression observed in tonic smooth muscles.
Batts
Timothy W
TW
Cardiovascular Division, Department of Internal Medicine, University of Virginia, Charlottesville, Virginia 22908, USA. TB3B@virginia.edu
Walker
John S
JS
Murphy
Richard A
RA
Rembold
Christopher M
CM
D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D002217:Carbachol / Q000494:pharmacology; D002339:Carotid Arteries / Q000378:metabolism; D005576:Colforsin / Q000494:pharmacology; D006152:Cyclic GMP / Q000031:analogs & derivatives / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D050886:HSP20 Heat-Shock Proteins / Q000172:deficiency* / Q000378:metabolism; D007158:Immunologic Techniques; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology*; D018994:Myosin Light Chains / Q000378:metabolism; D010766:Phosphorylation; D011817:Rabbits; D013194:Staining and Labeling; D013552:Swine; D001743:Urinary Bladder / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*
D050886:HSP20 Heat-Shock Proteins; D018994:Myosin Light Chains; D005576:Colforsin; C016276:8-bromocyclic GMP; D002217:Carbachol; D000262:Adenylyl Cyclases; D006152:Cyclic GMP; D007545:Isoproterenol