Mammals and birds have independently evolved the 4-chambered hearts: : Analysis of connectin which works as molecular spring in striated muscle

Abstract

Mammals and birds have 4-chambered hearts and fully separated pulmonary and systemic circulation. Cardiac tissues in extant vertebrates are divided into two types, compact and spongy myocardium, which are associated with blood supply systems i.e. coronary and sinusoidal circulation respectively. Mammals and birds have the hearts with coronary circulation with diastolic predominant flow due to ventricular compression during systole. We examined whether compact myocardium had a stiffer mechanical property compared with spongy myocardium to maintain diastolic coronary flow, and gene and amino acid sequence of molecular spring connectin that regulates ventricular mechanical property.The hearts of rats and chickens were significantly stiffer than those of frogs. The lengths of elastic segments of connectin in mice and chickens were shorter, with different regulatory mechanisms, than those in frogs . These results showed that mammals and birds evolved the strong 4-chambered hearts independently in adapting to oxygen environment.