Integrity of Energy Stores in Cat Papillary Muscle

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Abstract
Although isolated cat papillary muscles have proved useful in a variety of physiologic and pharmacologic studies, the energy integrity of this preparation has been questioned. Accordingly, papillary muscles (avg diam = 1.3 mm) were either placed in oxygenated Krebs solution for 1 hour at 26°C at rest or were made to contract at various frequencies and temperatures and for various durations. In addition, samples of right ventricular muscle were obtained from living cats. Specimens were frozen in liquid nitrogen-cooled isopentane for determination of ATP and creatine phosphate (CP). In vivo CP + ATP of right ventricular muscle was 12.9±0.8 µmoles/g. In papillary muscles at rest, CP + ATP was 16.7±0.6 µmoles/g, significantly higher than right ventricular muscle in vivo (P <.01). In vitro at 12 contractions/minute, CP + ATP was 16.0±1.0 µmoles/g, not different from resting papillary muscles but higher than in vivo stores in right ventricular muscle. At 30 or 60 contractions/minute, CP + ATP was reduced to 13.7±1.1 and 11.1±0.7 µmole/g. Neither increasing the in vitro temperature from 26° to 37°C, nor extending the duration of stimulation from 1 to 3 hours at 12/minute significantly altered CP + ATP. It is concluded that the energy stores in papillary muscles, even of moderately large diameter, are intact for at least 3 hours while contracting at frequencies of 12/minute at 26°C. Further, energy stores of papillary muscle are even greater than those found in right ventricular muscle in vivo. While muscle is contracting at 30 or 60/minute, its energy stores may be slightly limited.