Changes in isoform composition, structure, and functional properties of titin from Mongolian gerbil (Meriones unguiculatus) cardiac muscle after space flight.

Changes in isoform composition, secondary structure, and titin phosphorylation in Mongolian gerbil (Meriones unguiculatus) cardiac muscle were studied after 12-day-long space flight onboard the Russian spacecraft Foton-M3. The effect of titin on the actin-activated myosin ATPase activity at pCa 7.5 and 4.6 was also studied. Almost twofold increase in titin long N2BA isoform content relative to that of short N2B isoform was found on electrophoregrams of cardiac muscle left ventricle of the flight group gerbils. Differences in secondary structure of titin isolated from cardiac muscle of control and flight groups of gerbils were found. An increase in phosphorylation (1.30-1.35-fold) of titin of cardiac muscle of the flight group gerbils was found. A decrease in activating effect of titin of cardiac muscle of the flight group gerbils on actomyosin ATPase activity in vitro was also found. The observed changes are discussed in the context of M. unguiculatus cardiac muscle adaptation to conditions of weightlessness.