The 1.3 isoform of Na+-Ca 2+ exchanger expressed in guinea pig tracheal smooth muscle is less sensitive to KB-R7943.
The sodium-calcium exchanger (NCX) plays a major role in the regulation of cytosolic Ca(2+) in muscle cells. In this work, we performed force experiments to explore the role of NCX during contraction and relaxation of Cch-stimulated guinea pig tracheal smooth muscle strips. This tissue showed low sensitivity to NCX inhibitor KB-R7943 (IC50, 57 +/- 2 microM), although a complete relaxation was obtained by NCX inhibition at 100 microM. Interestingly, relaxation after washing the agonist was prolonged in the absence of external Na(+), whereas washing without Na(+) and in the presence of KB-R7943 resembled control conditions with physiological solution. Altogether, this suggests the reversal of NCX to a Ca(2+) influx mode by the manipulation on the Na(+) gradient, which can be inhibited by KB-R7943. In order to understand the low sensitivity to KB-R7943, we studied the molecular aspects of the NCX expressed in this tissue and found that the isoform of NCX expressed is 1.3, similar to that described in human tracheal smooth muscle. Sequencing revealed that amino acid 19 in exon B is phenylalanine, whereas in its human counterpart is leucine, and that the first amino acid after exon D is aspartate instead of glutamate in humans. Results herein presented are discussed in term of their possible functional implications in the exchanger activity and thus in airway physiology.
Algara-Suárez
Paola
P
Department of Physiology, Facultad de Medicina de la Universidad Autónoma de San Luis Potosí, Av. V. Carranza 2405, San Luis Potosí, San Luis Potosí 78210, Mexico.
Mejía-Elizondo
Rebeca
R
Sims
Stephen M
SM
Saavedra-Alanis
Victor M
VM
Espinosa-Tanguma
Ricardo
R
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002118:Calcium / Q000378:metabolism; D006168:Guinea Pigs; D008297:Male; D008969:Molecular Sequence Data; D009119:Muscle Contraction / Q000187:drug effects*; D009126:Muscle Relaxation / Q000187:drug effects; D032389:Myocytes, Smooth Muscle / Q000378:metabolism; D020033:Protein Isoforms / Q000378:metabolism; D019831:Sodium-Calcium Exchanger / Q000037:antagonists & inhibitors / Q000378:metabolism*; D013890:Thiourea / Q000031:analogs & derivatives* / Q000494:pharmacology; D014132:Trachea / Q000378:metabolism
C101670:2-(2-(4-(4-nitrobenzyloxy)phenyl)ethyl)isothiourea methanesulfonate; D020033:Protein Isoforms; D019831:Sodium-Calcium Exchanger; D013890:Thiourea; D002118:Calcium