VOL. 4 (1950) 



CONTRACTILITY OF A NON-CONDUCTING FIBER 



63 



TABLE III 



INHIBITION OF ATP INDUCED CONTRACTION IN NON-CONDUCTING MUSCLE FIBERS (rABBIT) BY SOME 

 COMPOUNDS REACTING WITH -SH GROUPS. AFTER EXPOSURE THE FIBERS WERE SOAKED IN SALINE 

 CONTAINING O.OI M CYSTEINE EXCEPT IN THE CASE OF MAPHARSEN IN WHICH SALINE ALONE PROVED 



TO BE EFFECTIVE 



inhibition of contraction. At a concentration of i-io"^ M, however, the inhibitory 

 effect of this compound appeared negHbible. 



Other compounds tested and found without an inhibitory effect on the contractile 

 process were sodium monoiodoacetate i-io"^ M, sodium pyrophosphate 4.4- lo"^ M, 

 sodium arsenate 3-io~^ M, sodium arsenite i-io"^ M and antimony, tartrate and 

 chloride, 8- 10-2 M. 



Since o-iodosobenzoate is a reversible inhibitor of contraction, the following ex- 

 periments were carried out. Thirty fiber units 6-8 cm in length were placed in a solution 

 of o-iodosobenzoate 5 • io~* M in saline. At various intervals 2 cm were cut from seme 

 of these fibers, and the sections tested for contractility in a standard ATP solution 

 I- io~2 M. After 40 minutes, none of the parts of the fibers so tested contracted on ex- 

 posure to the ATP standard. The fibers were then removed from the inhibiting solution. 

 Ten were placed in saline containing cysteine in i • lO"^ M, the remainder in ATP 

 i-io~2 M for either 2 or 10 minutes. The experimental groups which did not contract 

 during exposure to ATP were removed from the ATP and washed in saline for 10 minutes 

 and then soaked in saline with i • lO"^ M cysteine for 12 hours. The fibers placed directh^ 

 in the cysteine saline solution were tested by removing a unit and exposing it to ATP 



1 • io~2 M. Contractility had returned in go minutes. The fibers which were soaked either 



2 or 10 minutes in ATP prior to their transfer into the cysteine saline were tested for 

 return of contractility in a manner similar to the former group. During the 12 hours 

 of observation, measurable shortening responses did not appear. 



When fibers soaked in o-iodosobenzoate i • lO"^ M ceased to contract, they were 

 washed in sahne for 10 minutes and homogenized. At that period, the ATPase activity 

 of their homogenates ranged from 3-5 //g P/mg/15 min. A part of the saline washed 

 fibers were then regenerated in a solution of cysteine i • lO""^ M. At the earliest moment 

 when contractility returned, the homogenate revealed an ATPase activity of 5.5-8 

 iWg P/mg/15 min. 



Fibers preserved in glycerol and then soaked in cold saline for 10 days retained their 

 ability to contract when their ATPase activity was 6 //g P/mg/15 min or above. 

 Below this level contraction was absent. 



Effect of biologically active compounds 



Fibers were exposed for 30 to 60 minutes to a number of substances known to 

 have an effect on the contraction of normal muscle. In Table IV are listed the compounds 



References p. 6y. 



