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1.  Absence of force suppression in rabbit bladder correlates with low expression of heat shock protein 20 
BMC Physiology  2005;5:16.
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.
Isometrically mounted mucosa free rabbit bladder strips were contracted with carbachol and relaxed with 8-Br-cGMP, forskolin, or isoprenaline.
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).
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.
PMCID: PMC1285364  PMID: 16266435
2.  Heat induced HSP20 phosphorylation without increased cyclic nucleotide levels in swine carotid media 
BMC Physiology  2003;3:3.
Heat pretreatment of swine carotid artery has been shown to increase ser16-heat shock protein 20 (HSP20) phosphorylation and suppress force, i.e., reduce force with only minimal reduction in ser19-myosin regulatory light chain (MRLC) phosphorylation.
We further investigated this response in intact histamine stimulated swine carotid artery rings. There was a heat threshold such that increased ser16-HSP20 phosphorylation and force suppression were observed between 43°C and 46°C. The increased ser16-HSP20 phosphorylation persisted up to 16 hours after 44.5°C heat treatment. Pretreatment of swine carotid media at 44.5°C increased ser16-HSP20 phosphorylation without increases in [cAMP] or [cGMP], suggesting an alternate mechanism, perhaps phosphatase inhibition, for the increase in ser16-HSP20 phosphorylation. Heat pretreatment at 47.5°C reduced force by decreasing MRLC phosphorylation rather than by large increases in ser16-HSP20 phosphorylation. HSP20 phosphorylation at the putative PKC site did not change with any treatment.
These results demonstrate that multiple mechanisms can induce force suppression that is correlated with ser16-HSP20 phosphorylation: 1) nitrovasodilators via cGMP, 2) forskolin via cAMP, and 2) thermal stress in a cyclic nucleotide independent manner.
PMCID: PMC155685  PMID: 12716456
cyclic AMP; cyclic GMP; heat shock proteins; vascular smooth muscle
3.  Localization of heat shock protein 20 in swine carotid artery 
BMC Physiology  2001;1:10.
Cyclic nucleotides can relax vascular smooth muscle by mechanisms distal to myosin regulatory light chain (MRLC) phosphorylation. This mechanism, termed relaxation without MRLC dephosphorylation, may be regulated by ser16 phosphorylation of heat shock protein 20 (HSP20).
Confocal imaging of HSP20 in smooth muscle tissues revealed that HSP20 was present throughout the cytoplasm, although some focal regions of the cytoplasm were found to contain more HSP20 than the remaining cytoplasm. The distribution of HSP20 within the cytoplasm was not altered by histamine, forskolin, or nitroglycerin.
Cytoplasmic localization of HSP20 is consistent with a potential function of HSP20 as a regulator of smooth muscle contractile force.
PMCID: PMC48151  PMID: 11532202

Results 1-3 (3)