Non-sense mutations in the dihydropyridine receptor β1 gene, CACNB1, paralyze zebrafish relaxed mutants

• Published in: Cell calcium (Edinburgh) Vol. 39; no. 3; pp. 227 - 236
• Main Authors: Zhou, Weibin, Saint-Amant, Louis, Hirata, Hiromi, Cui, Wilson W., Sprague, Shawn M., Kuwada, John Y.
• Format: Journal Article
• Language: English
• Published: Elsevier India Pvt Ltd 2006
• Subjects: Dihydropyridine receptor; EC coupling; Muscle; Voltage-dependent calcium channel; Zebrafish; Zebrafish; EC coupling; Muscle; Voltage-dependent calcium channel; Dihydropyridine receptor
• ISSN: 0143-4160; 1532-1991
• DOI: 10.1016/j.ceca.2005.10.015

Contractions by skeletal muscle require proper excitation–contraction (EC) coupling, whereby depolarization of the muscle membrane leads to an increase in cytosolic Ca 2+ and contraction. Changes in membrane voltage are detected by dihydropyridine receptors (DHPR) that directly interact with and activate ryanodine receptors to release Ca 2+ from the sarcoplasmic reticulum into the cytosol. A genetic screen for motility mutations isolated a new allele of the immotile zebrafish mutant relaxed. Muscles in relaxed embryos do not contract in response to potassium chloride (KCl) thus appear unresponsive to membrane depolarization, but do contract when stimulated by caffeine, an agonist of ryanodine receptors. This suggests that relaxed mutant muscles are defective in EC coupling. Indeed, immunohistochemical analysis demonstrated that mutants lack DHPRs in skeletal muscles. The mutant phenotype results from non-sense mutations in the zebrafish CACNB1 gene that encodes the DHPR β1 subunit. The zebrafish CACNB1 gene is expressed in skeletal muscles, PNS and CNS. Electrophysiological recordings showed no obvious abnormalities in the motor output of relaxed mutants, presumably due to redundancy provided by other β subunits. The structural and functional homology of CACNB1 in zebrafish and mammals, suggests that zebrafish can be useful for studying EC coupling and potential neuronal function of CACNB1.