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HANDBOOK OF PHYSIOLOGY 



( IRCI1.ATION II 



120" 



o 100- 





o 



12 3 4 5 12 3 4 5 6 



fig. g. Fluctuations of tension {broken line) and of radioactivity (K. 12 ) appearing in washing solu- 

 tion (continuous line) of taenia coli during spontaneous activity .4, before. B, in the presence of atro- 

 pine 2 X io -6 . [From Born & Biilbring (16).] 



--110 



--90 m 



3 



o 



adding measurements of ionic exchange to the simul- 

 taneous monitoring of tension and electrical activity. 

 By restricting their attempt to the simpler problem 

 of measuring only K they succeeded quite elegantly 

 and in so doing proved beyond doubt that basic ionic 

 theory is generally valid, at least for the gut strip. 

 They used K 42 as tracer and analyzed the medium 

 flowing past the tissue. Spontaneous activity was 

 characterized by the parallel rise and fall of K efflux 

 and tension so that as tension rose, K efflux increased 

 and as tension fell, K efflux decreased. Similarly, 

 histamine and acetylcholine produced contraction 

 associated with a parallel increase in K efflux. Epi- 

 nephrine, which causes relaxation of this particular 

 preparation, seemed to do so by increasing K influx. 

 The fall in membrane potential previously observed 

 to parallel the increase in tension was evidently asso- 

 ciated with an ionic shift here measured as K efflux. 

 Presumably, if it had been technically feasible to 

 measure, a primary sodium influx would have been 

 recorded. 



Born (15) then turned to a study of some of the 

 metabolic problems concerned with contraction in 

 smooth muscle and for the first time we find a firm 

 separation of the relatively rapid changes in tension 

 from the maintained changes which we recognize as 

 tonus. The position is best stated by the author: "The 

 development of tension by smooth muscle involves 

 two mechanisms. One mechanism is responsible for 



the immediate rise in tension which occurs when the 

 muscle is stimulated and this mechanism continues 

 to function in anoxia and in the presence of 2:4 

 dinitrophenol. The other mechanism is responsible for 

 the sustained tension which the muscle shows, both 

 spontaneously and following stimulation. This mecha- 

 nism is abolished when metabolism is interfered with, 

 e.g., by depriving the muscle of glucose or of oxygen, 

 or by exposing it to 2:4 dinitrophenol." 



Later studies of electrical activity have rather 

 tended to cloud the picture. Biilbring & Ltillman (22) 

 demonstrated that spike frequency and tension could 

 be dissociated. Using dinitrophenol they showed that 

 spike frequency could be made to increase or decrease 

 without particular reference to tension changes. The 

 inverse relation of tension to membrane potential still 

 held under these circumstances, however, so that at 

 this point we might tend to disregard spike activity. 

 This idea is reinforced by Holman's observation (117) 

 that the addition of KC1 to the medium bathing a 

 taenia coli strip increases tension and decreases the 

 membrane potential. Further, at concentrations above 

 20 meq per liter, the relation of K„ to membrane 

 potential is linear with a 33 mv slope per log unit 

 change, an important fit with ionic theory although 

 the low slope remains to be accounted for. 



Burnstock & Straub (26) using an improved pro- 

 cedure, the sucrose-gap technique, verified the fact 

 that K salts produced a membrane depolarization, 



