Stimulation of two metabotropic glutamate-receptor subtypes, mGluR1 and mGluR5, triggers the release of Ca2+ from intracellular stores through the inositol-(1,4,5) trisphosphate (InsP3) pathway. Here we report that glutamate induces single-peaked intracellular Ca2+ mobilization in mGluR1alpha-transfected cells but elicits Ca2+ oscillations in mGluR5a-transfected cells. The response patterns of the intracellular Ca2+ increase depend upon the identity of a single amino acid, aspartate (at position 854) or threonine (at position 840), located within the G-protein-interacting domains of mGluR1alpha and mGluR5a, respectively. Pharmacological and peptide mapping analyses indicated that phosphorylation of the threonine residue at position 840 of mGluR5a by protein kinase C (PKC) is responsible for the generation of Ca2+ oscillations in mGluR5a-expressing cells. To our knowledge this is the first evidence that PKC phosphorylation of G-protein-coupled receptors is important in producing oscillations in intracellular Ca2+ signalling.

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An experimental survey of the strain energy density function of an isoprene rubber vulcanízate is carried out by biaxial extension of a sheet specimen. The first derivatives of the strain energy density function with respect to Ix and I2 are obtained from the biaxial stress-strain measurement, where Ix and 12 are the first and the second invariants of Green's deformation tensor, respectively. The measurement of these derivatives is done over a wide range of biaxial deformation, 3.005 < Ix < 20 and 3.005 < I2< 90, in the temperature range 273-353 K. Special care has been taken with the stress and strain measurements in the relatively small deformation region in order to prevent error in the derived values of the derivatives of the strain energy density function. From the result, it is concluded that the strain energy density function should be given by the sum of the two separate terms: W = CT(IX -3) + 6(IXJ2). It has been found that both 9ß/ and ßß/3 2 are more sensitive to changes in I2 than in Ix and the value of ß( ^accounts for, in the case of Ix = I2 = 10, for example, 32.5% of the whole strain energy density W.

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