CHANGES IN THE ELASTIC PROPERTIES OF CHOLINERGIC SYNAPTIC VESICLES ASMEASURED BY ATOMIC-FORCE MICROSCOPY

Cholinergic synaptic vesicles from Torpedo californica have been probe d with the atomic force microscope in aqueous buffers to map and measu re their elastic properties. Elastic properties were mapped with a new atomic force microscope technique known as force mapping. Force mappi ng of vesicles showed that the centers of the vesicles are harder or s tiffer than the peripheral areas in the three buffers that were invest igated. These were an isoosmotic buffer, a hypoosmotic buffer, and an isoosmotic buffer with 5 mM CaCl2 added. The hardness of the vesicular centers was quantified by calculation of the elastic modulus. Elastic moduli were in the range of 2-13 x 10(5) Pa. Vesicular centers were h ardest in calcium-containing buffer and softest in isoosmotic buffer. Hypotheses are presented for the composition and function of the hard centers.