| 1. |
- Mulvany, M J, et al.
(författare)
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Potentiating and depressive effects of ouabain and potassium-free solutions on rat mesenteric resistance vessels.
- 1982
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Ingår i: Circulation research. - 0009-7330. ; 51:4, s. 514-24
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated the in vitro effects of ouabain and K-free solutions on some pharmacological and electrophysiological properties of rat mesenteric resistance vessels (internal diameter approximately 190 micrometers). Vessels were mounted as ring preparations on a myograph capable of measuring their isometric wall tension. In normal saline solutions, vessels did not exhibit any tone and had a membrane potential of -54 mV. Both 1 mM ouabain and K-free solutions caused a transient depolarization of 5-8 mV; thereafter the membrane slowly depolarized to about -45 mV after 30 minutes. There was no mechanical response to ouabain, but K-free solutions caused a transient development of tension which could be inhibited by phentolamine (1 microM). In norepinephrine-activated vessels, exposure to ouabain or K-free solutions caused a small depolarization and an increase in tension. Long-term (30-minute) exposure to 1 mM ouabain or K-free solutions reduced the amplitude of norepinephrine responses and, for the lower (but not the higher) norepinephrine concentrations, the membranes were about 14 mV more depolarized than control. The mechanical responses to a cocktail of norepinephrine in a high potassium solution were, however, unaffected. Re-exposure to normal saline solution produced a transient hyperpolarization and transiently eliminated the norepinephrine response, but thereafter the membrane potential and response returned to normal. The results indicate that ouabain and K-free solutions can have both short-term potentiating and long-term depressive effects on the mechanical response of rat mesenteric resistance vessels to norepinephrine.
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| 2. |
- Mulvany, M J, et al.
(författare)
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Role of membrane potential in the response of rat small mesenteric arteries to exogenous noradrenaline stimulation.
- 1982
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Ingår i: The Journal of physiology. - 0022-3751. ; 332, s. 363-73
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Tidskriftsartikel (refereegranskat)abstract
- 1. We have made simultaneous measurements of membrane potential and wall tension in rat 200 microns mesenteric arteries. 2. The resting membrane potential was -59.2 +/- 0.4 mV and stable (218 measurements, fifty-two vessels). 3. With maximal exogenous noradrenaline stimulation (10 microM) the membrane depolarized to about -34 mV. During the onset of tension development oscillations (period about 6 sec) in both tension and membrane potential were often seen; the membrane potential changes led the tension changes by about 1.2 sec. 4. In the presence of increased K+ (e.g. 40 mM), vessels had an increased noradrenaline sensitivity, and here noradrenaline stimulation produced little change in membrane potential. 5. With maximal K+ stimulation (85 mM), in the presence of phentolamine (1 microM), the membrane depolarized to about -17 mV, the tension being about 70% of the maximal noradrenaline response. 6. In the presence of phentolamine (1 microM), noradrenaline caused hyperpolarization without tension development. The hyperpolarization was inhibited by propranolol and mimicked by isoprenaline. 7. The results suggest that in these small vessels membrane potential variations are not essential to, but have an important modulating influence on, the tension response to exogenous noradrenaline.
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| 3. |
- Mulvany, M J, et al.
(författare)
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Are isolated femoral resistance vessels or tail arteries good models for the hindquarter vasculature of spontaneously hypertensive rats?
- 1982
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Ingår i: Acta physiologica Scandinavica. - : Wiley. - 0001-6772 .- 1365-201X. ; 116:3, s. 275-83
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated the extent to which the properties of small arteries from the hindquarters of spontaneously hypertensive rats (SHRs) are consistent with the characteristics of perfused SHR hindquarter preparations (for which the relaxed vascular resistance, the reactivity and the sensitivity are reported to be increased). We have therefore compared the in vitro morphological and pharmacological properties of a femoral resistance vessel (i.d. ca 200 microns) and of the tail artery (i.d. ca 600 microns) from SHRs with those from control Wistar-Kyoto rats (WKYs). When relaxed, for any given wall tension, the internal circumference of the SHR resistance vessels was reduced, but that of the SHR tail artery was normal. When activated with 10 microM noradrenaline, the SHR resistance vessels had an increased calcium sensitivity, but the calcium sensitivity of the SHR tail arteries was normal. However, the maximum response of both types of SHR vessels was such that the vessels would have been able to contract against increased transmural pressure. The noradrenaline sensitivity of the SHR resistance vessels was normal but the SHR tail arteries had a decreased sensitivity. The results suggest that the femoral resistance vessel is in general a better model for the hindquarter vasculature than the tail artery.
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