ABSTRACT
The role of h1-calponin in regulating the contractile properties of smooth muscle was investigated in bladder and vas deferens of mice carrying a targeted mutation in both alleles designed to inactivate the basic calponin gene. These calponin knockout (KO) mice displayed no detectable h1-calponin in their smooth muscles. The amplitudes of Ca2+ sensitization, force and Ca2+ sensitivity were not significantly different in permeabilized smooth muscle of KO compared with wild-type (WT) mice, nor were the delays in onset and half-times of Ca2+ sensitization, initiated by flash photolysis of caged GTPgammaS, different. The unloaded shortening velocity (Vus) of thiophosphorylated fibres was significantly (P<0.05) faster in the smooth muscle of KO than WT animals, but could be slowed by exogenous calponin to approximate WT levels; the concentration dependence of exogenous calponin slowing of Vus was proportional to its actomyosin binding in situ. Actin expression was reduced by 25-50%, relative to that of myosin heavy chain, in smooth muscle of KO mice, without any change in the relative distribution of the actin isoforms. We conclude that the faster Vus of smooth muscle of the KO mouse is consistent with, but does not prove without further study, physiological regulation of the crossbridge cycle by calponin. Our results show no detectable role of calponin in the signal transduction of the Ca2+-sensitization pathways in smooth muscle.
Subject(s)
Calcium-Binding Proteins/deficiency , Muscle Contraction/physiology , Muscle Proteins/metabolism , Muscle, Smooth/physiology , Animals , Calcium/physiology , Calcium-Binding Proteins/genetics , Calcium-Binding Proteins/pharmacology , Contractile Proteins/metabolism , Male , Mesenteric Veins/ultrastructure , Mice , Mice, Knockout/genetics , Microfilament Proteins , Muscle Contraction/drug effects , Muscle Relaxation/physiology , Muscle, Smooth/ultrastructure , Reference Values , Time Factors , Urinary Bladder/ultrastructure , Vas Deferens/ultrastructure , CalponinsABSTRACT
The clinical findings of a kindred with an X-linked disorder are characterized by autoimmune polyendocrinopathy, enteropathy with villous atrophy, chronic dermatitis, and variable immunodeficiency. Linkage analysis was performed on 20 members of the affected kindred to determine the location of the responsible locus. Informative recombinations limited the region to an approximate 20 cM interval bordered by DXS1055 and DXS1196/DXS1050. Multipoint analysis generated a lod score >3 for the region contained between DXS8024 and DXS8031. The candidate region includes the Wiskott-Aldrich syndrome (WAS) locus. Evaluation of the Wiskott-Aldrich syndrome protein gene by single strand conformational analysis, heteroduplex analysis, and direct sequencing of the 12 exons in an affected male and two carrier females revealed no abnormalities. We conclude that this kindred has an X-linked disorder, distinct from WAS, that results in autoimmunity and variable immunodeficiency. The responsible locus maps to the pericentromeric region Xp11.23 to Xq21.1.
