Is High Concentration of Parvalbumin a Requirement for Superfast Relaxation?

J Muscle Res Cell Motil. 2009;30(1-2):57-65. doi: 10.1007/s10974-009-9175-z. Epub 2009 Apr 23.

Abstract

It is generally thought that the rapid relaxation of fast muscles is facilitated by the Ca(2+) binding protein parvalbumin (Parv). Indeed superfast swimbladder (SWB) muscle of toadfish contains the largest concentration of this protein ever observed (up to 1.5 mM). At 15 degrees C toadfish perform a 100 Hz call, 400 ms in duration, followed by a long (5-15 s) intercall interval. It has been proposed that Parv helps sequester the Ca(2+) during the call, and then Ca(2+) unbinds and is pumped back into the sarcoplasmic reticulum during the long intercall interval. Midshipman (Porichthys notatus) is another fish which calls at a high frequency; 80-100 Hz at a temperature of 12-15 degrees C. However, unlike toadfish, midshipman call with a 100% duty cycle. Without an intercall interval, Parv would seem of little use as it would become saturated early in calling. Here we show that the midshipman SWB has only about 1/8th of the Parv in toadfish. Moreover, total Parv content in calling male midshipman SWB was not different from that in the non-calling female and the much slower locomotory muscles. These data suggest that Parv does not play a large role in the calling of midshipman, which is accomplished without a high concentration of this protein. Native gel-electrophoresis also revealed presence of three major (PA-I, PA-II and PA-III) and two minor (PA-Ia and PA-IIIa, <5% of total content) Parv isoforms in adult toadfish SWB. Midshipman SWB contained about equal amounts of PA-I and PA-II and also a small (approximately 10%) amount of PA-III. By amino acid composition, toadfish PA-Ia and PA-I isoforms were different from PA-II and PA-III isoforms (by 24 and 14 residues, respectively).

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Air Sacs / chemistry
  • Air Sacs / metabolism
  • Amino Acid Sequence
  • Animals
  • Batrachoidiformes / metabolism*
  • Blotting, Western
  • Chromatography, Ion Exchange
  • Electrophoresis, Gel, Two-Dimensional
  • Female
  • Fish Proteins / analysis
  • Fish Proteins / metabolism*
  • Male
  • Muscle Fibers, Fast-Twitch / metabolism
  • Muscle Fibers, Fast-Twitch / physiology
  • Muscle Relaxation*
  • Parvalbumins / analysis
  • Parvalbumins / metabolism*
  • Protein Isoforms / analysis
  • Protein Isoforms / metabolism

Substances

  • Fish Proteins
  • Parvalbumins
  • Protein Isoforms