Changes in thyroid state affect pHi and Nai+ homeostasis in rat ventricular myocytes.

Abstract

We have tested the hypothesis that thyroid state may influence both the flow of cellular Ca2+ and the myofilament response to Ca2+ by effects on intracellular pH (pHi) and Na+ (Nai+). Single cardiac myocytes isolated from hypothyroid, euthyroid and hyperthyroid animals were loaded with fura-2/AM (Cai2+ probe), BCECF/AM (pHi probe) or SBFI/AM (Nai+ probe). Compared with hypothyroid animals, myocytes isolated from hyperthyroid rat hearts demonstrated a significant: (1) increase in extent of shortening; (2) decrease in the time to peak contraction; (3) increase in the peak amplitude of the fura-2 fluorescence ratio; (4) decrease in pHi (DeltapHi=0. 19+/-0.05); and (5) increase in Nai+ (DeltaNai+=2.88+/-0.55 mM). We have also compared pHi in Langendorff perfused hypo- and hyperthyroid rat hearts using NMR. We have found that hyperthyroid hearts are 0.15+/-0.03 pH units more acidic than hypothyroid hearts. Analysis of mRNA levels demonstrated that hyperthyroidism increased expression of both the Na+/Ca2+ exchanger and Na+/H+ antiporter, and decreased expression of Na+ channel mRNAs. These changes appear partially responsible for the observed changes in Nai+ and pHi. Our results provide the first evidence that changes in cardiac contractility associated with altered thyroid state not only involve effects on Ca2+, but may also involve changes in the response of the myofilaments to Cai2+mediated by altered pHi and Nai+.

• Authors: B M Wolska, V Averyhart-Fullard, A Omachi, M O Stojanović, R G Kallen, R J Solaro
• Journal: Journal of molecular and cellular cardiology (J Mol Cell Cardiol) Vol. 29 Issue 10 Pg. 2653-63 (Oct 1997) ISSN: 0022-2828 [Print] England
• PMID: 9344760 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't, Research Support, U.S. Gov't, P.H.S.)
• Copyright: Copyright 1997 Academic Press Limited.

Chemical References

• RNA, Messenger
• Sodium Channels
• Sodium-Calcium Exchanger
• Sodium-Hydrogen Exchangers
• Thyroid Hormones
• Sodium
• Calcium

Topics

• Animals
• Calcium (metabolism)
• Heart Ventricles (cytology, metabolism)
• Homeostasis
• Hydrogen-Ion Concentration
• Hyperthyroidism (metabolism)
• Hypothyroidism (metabolism)
• Male
• Myocardial Contraction
• Myocardium (metabolism)
• RNA, Messenger
• Rats
• Rats, Sprague-Dawley
• Sodium (metabolism)
• Sodium Channels (genetics, metabolism)
• Sodium-Calcium Exchanger (metabolism)
• Sodium-Hydrogen Exchangers (metabolism)
• Thyroid Gland (metabolism)
• Thyroid Hormones (metabolism)