Homogenates of baby-hamster kidney cells and rat embryo fibroblasts prepared by nitrogen cavitation contain a small population of slowly sedimenting mitochondria or mitochondrial fragments, which contaminate the microsomal fraction. This appears to limit the resolution of surface membrane and endoplasmic reticulum on magnesium-containing dextran gradients. The microsomal material and mitochondria can, however, be completely separated on a 10-60% (w/w) sucrose zonal gradient containing a 30% sucrose plateau. On magnesium-containing dextran gradients this mitochondria-free microsomal material can be resolved into at least two surface membrane fractions and at least two endoplasmic reticulum fractions. Comparison of polyoma virus-transformed and normal baby-hamster kidney cells reveals some interesting differences in their microsomal fractionation patterns and the characteristics of the Na(+)/K(+)-Mg(2+) adenosine triphosphatase of their surface membranes, in particular a tenfold lower K(m) in the virus-transformed cells. The fractionation patterns of normal and spontaneously transformed rat embryo fibroblasts are also briefly discussed, particularly in relation to the significance of the observation that both the surface membrane and endoplasmic reticulum from these cells can be subfractionated.

Adenosine Triphosphatases↗

PubMed1972

Differences in sensitivity to vasoconstrictor drugs within the wall of the sheep carotid artery.

1. Controlled heat damage was used to separate the responses of the outer innervated smooth muscle from those of the inner nerve-free smooth muscle of the sheep carotid artery.2. Preparations of smooth muscle from the inner part of the media gave 50% maximal contractions in response to approximately 1/15 the concentration of noradrenaline needed to produce similar responses from outer smooth muscle. The difference in sensitivity was greater in the lower than the upper parts of the dose-response curves.3. Much of the difference in sensitivity was still seen in the presence of Desipramine and after chronic denervation, and so could not be attributed to uptake of noradrenaline by the nerve fibres in the outer smooth muscle; disappearance of the fibres after denervation was confirmed by fluorescence microscopy.4. Similar but generally smaller differences in sensitivity between inner and outer smooth muscle were seen with respect to histamine, angiotensin II and 5-hydroxytryptamine.5. Sympathetic denervation 10-14 days previously increased the sensitivity of outer strips to noradrenaline; it usually also increased their sensitivity to histamine, suggesting that the change largely represented non-specific denervation super-sensitivity.6. The high sensitivity of the inner smooth muscle is likely to be of value in enabling it to respond to the relatively low concentration of noradrenaline reaching it in life.

Angiotensin II↗

PubMed1971