Research article

Absence of force suppression in rabbit bladder correlates with low expression of heat shock protein 20

Timothy W Batts^1,2 , John S Walker² , Richard A Murphy² and Christopher M Rembold^1,2

¹Cardiovascular Division, Department of Internal Medicine, University of Virginia, Charlottesville, Virginia 22908 USA

²Department of Molecular Physiology and Cellular Biophysics, University of Virginia, Charlottesville, Virginia 22908 USA

author email corresponding author email

BMC Physiology 2005, 5:16doi:10.1186/1472-6793-5-16

Published:	2 November 2005

Abstract

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).

Conclusion

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.